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https://github.com/edson-acordi/4bit-microcomputer
MikroLeo project files (schematic, PCB, assembler, emulator/debugger, circuit simulation file, documentation, example of programs etc). MikroLeo is a 4-bit microcomputer developed mainly for educational purposes and distributed for free under open-source licenses.
https://github.com/edson-acordi/4bit-microcomputer
4-bit 74hctxxx alu asm assembler assembly-language computer cpu didactic digital-electronics education harvard-architecture logic-gates microcomputer nibble open-source oshw programming risc
Last synced: 4 months ago
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MikroLeo project files (schematic, PCB, assembler, emulator/debugger, circuit simulation file, documentation, example of programs etc). MikroLeo is a 4-bit microcomputer developed mainly for educational purposes and distributed for free under open-source licenses.
- Host: GitHub
- URL: https://github.com/edson-acordi/4bit-microcomputer
- Owner: edson-acordi
- License: other
- Created: 2020-01-18T16:14:22.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2024-02-29T21:02:02.000Z (11 months ago)
- Last Synced: 2024-09-30T06:04:39.253Z (4 months ago)
- Topics: 4-bit, 74hctxxx, alu, asm, assembler, assembly-language, computer, cpu, didactic, digital-electronics, education, harvard-architecture, logic-gates, microcomputer, nibble, open-source, oshw, programming, risc
- Language: Python
- Homepage:
- Size: 16.3 MB
- Stars: 58
- Watchers: 5
- Forks: 2
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE-CC-BY-SA-4.0.md
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README
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# MikroLeo #
## 4-bit Didactic Microcomputer ##
The hardware is finished and working.
However, it needs exhaustive testing over a long period to see if the hardware will fail when operating at full speed. It implies that if the hardware fails, the maximum clock speed must be reduced, for example, to 2.5 MHz.
This project was developed mainly for educational purposes.
I hope it will be a good learning platform for anyone who likes electronics, computers and programming.
Since my first attempts, many efforts have been made to make this project real.
It is aimed at students, enthusiasts, hackers, professors and anyone who wants to understand or improve their knowledge of electronics and learn how a simple computer works. In addition, it is also an attempt to rescue the story about the beginning of the development of integrated circuits and computers on a single chip, to demonstrate the capabilities that these machines had at that time.
It is a fully open-source hardware and software project that can be built at home. Only the printed circuit board (PCB) needs to be produced by some company.
For the next steps, an important thing is to make good documentation for MikroLeo!
***Support this project!***
***Help to promote and disseminate the knowledge.***
*Copyright (C) 2020-2024 MikroLeo Devs*
---
#### The KiCad project files have been uploaded! ####
1-[Download KiCad Project](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Kicad-files/MikroLeo/MikroLeo_v0.1901_KiCad.zip "download")
2-[Download Gerber Files](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Kicad-files/MikroLeo/Gerber/MikroLeo_v0.1901_Rev1.01A_Gerber.zip "download")
3-[Download the schematic diagram (pdf file)](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Kicad-files/MikroLeo/MikroLeo_v0.1901_Rev1.01A_sch.pdf "download")
4-[Download Bill of Materials (pdf file)](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Docs/MikroLeo_v0.1901_Rev1.01A_BOM.pdf "download")
└─>[Components list made by @vguttmann at the Mouser Electronics store](https://www.mouser.de/ProjectManager/ProjectDetail.aspx?State=EDIT&ProjectGUID=436f56c7-ebe0-469b-b287-6e751369f9cc)
---
#### A Python program to generate machine code has been uploaded ####
[Python code to "compile" asm files](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Compiler/MikroLeoAsm_20221130.py "download")
[Windows executable (.exe) to "compile" asm files](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Compiler/MikroLeoAsm_20221130.exe "download")
---
#### How to transfer compiled program to MikroLeo ####
[Download documentation (pdf file)](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Docs/How%20to%20transfer%20a%20compiled%20program%20to%20MikroLeo.pdf "download")
---
#### The Arduino program to transfer a compiled program to MikroLeo ####
[Code (Arduino IDE)](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Arduino/MikroLeo_Program_Writring.ino "download")
---
**Main Features**:
- Implements a 4 bit CPU
- 2k x 16 Program Memory (up to 4k)
- 2k x 4 RAM (up to 4k)
- 4 Output Ports (16 outputs)
- 4 Input Ports (16 inputs)
- Single Cycle Instruction/RISC
- Harvard Architecture
- 3 execution modes:
* step by step
* 3MHz (precise time base)
* adjustable - low clock speed ( $\approx$ 1 Hz - 200 Hz)
- No MPU/MCU or complex chips
- No microcode
- No stack
- Indirect addressing to facilitate the implementation of subroutines
- Program memory implemented with RAM to easy programming
- It can be programmed using physical input switches or via Arduino/Esp32
- It accepts 300 and 600 mils memories (for those with old DIP versions)
- Supercapacitor or battery to keep the program in RAM (for low power version)
- Built with 74HCTxxx integrated circuits for low power consumption and compatibility with TTL circuits
- All parts are through-hole for easy assembly
- All control signals, registers and the program counter are available through the pin header connectors
- Dual layer Single board with 295.9mm x 196.9mm
# MikroLeo Architecture #
Note that some buffers are used to allow viewing the contents of registers at any time, since this project is mainly intended for educational purposes.
Reset Vector: 0x000
# The MikroLeo Instruction Set #
Although MikroLeo has only 20 instructions, using the AMODE bit (b14) and the modifier bits (b13:b12), it is possible to encode 64 combinations of instructions, as can be seen below.
## Instruction Set explanation and examples ##
In binary, the Instruction Word is coded as,
ROMH (Most significant byte of program memory):
| b15 | b14 | b13| b12| b11 | b10 | b9 | b8
|---------|-----|----|----|------|------|------|------|
|MICRO2_IN|AMODE|MOD1|MOD0|MICRO3|MICRO2|MICRO1|MICRO0|
ROML (Least significant byte of program memory):
| b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 |
|------|------|------|------|--------|--------|--------|--------|
MAddr3|MAddr2|MAddr1|MAddr0|Operand3|Operand2|Operand1|Operand0|
$\text{\small\textcolor{brown}{- Note: b15 = bit15 ... b0 = bit0}}$
Below is more detailed information about the instruction word,
### Instruction Set Description ###
**LDI - Load with Immediate**
Description: Loads the operand value into a register.
Registers: ACC, RA, RB or RC
Operation: Register <─ Operand
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|----------------|
| 0x00Xn |0x00 | LDI ACC,n |ZF |
| 0x10Xn |0x10 | LDI RA,n |- |
| 0x20Xn |0x20 | LDI RB,n |- |
| 0x30Xn |0x30 | LDI RC,n |- |
Note:
The operand (immediate) is represented by the letter "n".
'X' (in capital letter) means it doesn't matter.
'x' (in lowercase) is used to represent a hexadecimal number.
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x0005 | LDI ACC,5 | Load ACC with operand n|
| 0x1006 | LDI RA,6 | Load RA with operand n|
| 0x2007 | LDI RB,7 | Load RB with operand n|
| 0x300a | LDI RC,10 | Load ACC with operand n|
The MAddr nibble is not used with this instruction, so it is left at 0.
The Instruction Word, for example, for LDI RA,6 is coded as,
```asm
0x1006
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 6
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 0
└─────> Most significant Nibble => HiNB[b15:b12] = 1
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0001 0000 0000 0110
┆ ┆ ┆ └──> Operand = 6
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 0 (OPCode)
└─────────────────> HiNB = 1 (MICRO2_IN = 0, AMODE = 0, MOD = 1)
```
**NAND - bitwise Nand**
Description: Performs the bitwise Nand operation between ACC with (Operand n, RA, RB or RAM).
The result is stored in ACC.
Operations:
ACC <─ ACC NAND Operand
ACC <─ ACC NAND Register
ACC <─ ACC NAND RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|----------------|
| 0x01Xn |0x01 | NAND ACC,n |ZF |
| 0x11XX |0x11 | NAND ACC,RA |ZF |
| 0x21XX |0x21 | NAND ACC,RB |ZF |
| 0x31mn |0x31 | NAND ACC,@RAM |ZF |
| 0x71XX |0x71 | NAND ACC,@R |ZF |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|---------------|-|
| 0x0105 | NAND ACC,5 | NAND operation between the accumulator and the operand and
stores it in ACC |
| 0x1100 | NAND ACC,RA | NAND operation between the accumulator and register RA and
stores it in ACC |
| 0x2100 | NAND ACC,RB | NAND operation between the accumulator and register RB and
stores it in ACC |
| 0x310a | NAND ACC,@0x0a | NAND the contents of the RAM address with ACC and stores it
in ACC. In this case, the RAM address = RC:0:a|
| 0x7100 | NAND ACC,@R | NAND the contents of the RAM address with ACC and stores it
in ACC. In this case, the RAM address = RC:RB:RA|
The Instruction Word, for example, for NAND ACC,5 is coded as,
```asm
0x0105
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 5
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 1
└─────> Most significant Nibble => HiNB[b15:b12] = 0
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0000 0001 0000 0101
┆ ┆ ┆ └──> Operand = 5
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 1 (OPCode)
└─────────────────> HiNB = 0 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**LDW - Load from RAM Memory**
Description: Loads the contents of RAM into ACC.
Operation: ACC <─ RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|---------------------|----------------|
| 0x02mn |0x02 | LDW ACC,@RAM |ZF |
| 0x42XX |0x42 | LDW ACC,@R |ZF |
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|---------------|-|
| 0x023b | LDW ACC,@0x3b |Loads the contents of the RAM address (RC:3:b) in ACC |
| 0x4200 | LDW ACC,@R |Loads the contents of the RAM address (RC:RB:RA) in ACC |
The Instruction Word, for example, for LDW ACC,@0x3b is coded as,
```asm
0x023b
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = b
┆┆└───> Second Nibble => MAddr[b7:b4] = 3
┆└────> Third Nibble => MICRO[b11:b8] = 2
└─────> Most significant Nibble => HiNB[b15:b12] = 0
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0000 0010 0011 1011
┆ ┆ ┆ └──> Operand = b
┆ ┆ └───────> MAddr = 3
┆ └────────────> MICRO = 2 (OPCode)
└─────────────────> HiNB = 0 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**LDA - Load Accumulator**
Description: Loads the contents of a register into the ACC.
Registers: RA, RB or RC
Operation: ACC <─ Register
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x13XX |0x13 | LDA RA |ZF |
| 0x23XX |0x23 | LDA RB |ZF |
| 0x33XX |0x33 | LDA RC |ZF |
Note: 'X' means it doesn't matter.
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x1300 | LDA RA | Load into ACC the content of RA |
| 0x2300 | LDA RB | Load into ACC the content of RB |
| 0x3300 | LDA RC | Load into ACC the content of RC |
The MAddr/LAddr nibble is not used with this instruction, so it is left at 0.
The Instruction Word, for example, for LDA RA is coded as,
```asm
0x1300
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 0
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 3
└─────> Most significant Nibble => HiNB[b15:b12] = 1
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0001 0011 0000 0000
┆ ┆ ┆ └──> Operand = 0 (For this instruction, it doesn't matter)
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 3 (OPCode)
└─────────────────> HiNB = 1 (MICRO2_IN = 0, AMODE = 0, MOD = 1)
```
**OUTA - Send to OUTA output port**
Description: Sends the operand/Register or RAM value to the OUTA output port.
Operations:
OUTA <─ Operand
OUTA <─ ACC
OUTA <─ RA
OUTA <─ RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x04Xn |0x04 | OUTA n |- |
| 0x14XX |0x14 | OUTA ACC |- |
| 0x24XX |0x24 | OUTA RA |- |
| 0x34mn |0x34 | OUTA @RAM |- |
| 0x74XX |0x74 | OUTA @R |- |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x0405 | OUTA 5 | Sends the operand to the OUTA port |
| 0x1400 | OUTA ACC | Sends the ACC to the OUTA port. |
| 0x2400 | OUTA RA | Sends the RA to the OUTA port. |
| 0x342a | OUTA @0x2a | Sends the content of RAM to the OUTA port. In this case, the
RAM address = RC:2:a|
| 0x7400 | OUTA @R | Sends the content of RAM to the OUTA port. In this case, the
RAM address = RC:RB:RA|
The Instruction Word, for example, for OUTA ACC is coded as,
```asm
0x1400
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 0
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 4
└─────> Most significant Nibble => HiNB[b15:b12] = 1
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0001 0100 0000 0000
┆ ┆ ┆ └──> Operand = 0
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 4 (OPCode)
└─────────────────> HiNB = 1 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**OUTB - Send to OUTB output port**
Description: Sends the operand/Register or RAM value to the OUTB output port.
Operations:
OUTB <─ Operand
OUTB <─ ACC
OUTB <─ RA
OUTB <─ RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x05Xn |0x05 | OUTB n |- |
| 0x15XX |0x15 | OUTB ACC |- |
| 0x25XX |0x25 | OUTB RA |- |
| 0x35mn |0x35 | OUTB @RAM |- |
| 0x75XX |0x75 | OUTB @R |- |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x0507 | OUTB 7 | Sends the operand to the OUTB port |
| 0x1500 | OUTB ACC | Sends the ACC to the OUTB port. |
| 0x2500 | OUTB RA | Sends the RA to the OUTB port. |
| 0x35f1 | OUTB @0xf1 | Sends the content of RAM to the OUTB port. In this case, the
RAM address = RC:f:1|
| 0x7500 | OUTB @R | Sends the content of RAM to the OUTB port. In this case, the
RAM address = RC:RB:RA|
The Instruction Word, for example, for OUTB 7 is coded as,
```asm
0x0507
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 7
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 5
└─────> Most significant Nibble => HiNB[b15:b12] = 0
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0001 0101 0000 0111
┆ ┆ ┆ └──> Operand = 7
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 5 (OPCode)
└─────────────────> HiNB = 0 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**OUTC - Send to OUTC output port**
Description: Sends the operand/Register or RAM value to the OUTC output port.
Operations:
OUTC <─ Operand
OUTC <─ ACC
OUTC <─ RA
OUTC <─ RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x06Xn |0x06 | OUTC n |- |
| 0x16XX |0x16 | OUTC ACC |- |
| 0x26XX |0x26 | OUTC RA |- |
| 0x36mn |0x36 | OUTC @RAM |- |
| 0x76XX |0x76 | OUTC @R |- |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x0607 | OUTC 0xf | Sends the operand to the OUTC port |
| 0x1600 | OUTC ACC | Sends the ACC to the OUTC port. |
| 0x2600 | OUTC RA | Sends the RA to the OUTC port. |
| 0x3683 | OUTC @0x83 | Sends the content of RAM to the OUTC port. In this case, the
RAM address = RC:8:3|
| 0x7600 | OUTC @R | Sends the content of RAM to the OUTC port. In this case, the
RAM address = RC:RB:RA|
The Instruction Word, for example, for OUTC @0x83 is coded as,
```asm
0x3683
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 3
┆┆└───> Second Nibble => MAddr[b7:b4] = 8
┆└────> Third Nibble => MICRO[b11:b8] = 6
└─────> Most significant Nibble => HiNB[b15:b12] = 3
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0011 0110 1000 0011
┆ ┆ ┆ └──> Operand = 3
┆ ┆ └───────> MAddr = 8
┆ └────────────> MICRO = 6 (OPCode)
└─────────────────> HiNB = 3 (MICRO2_IN = 0, AMODE = 0, MOD = 3)
```
**LDR - Loads a Register with the Accumulator.**
Description: Load the contents of the ACC into a register.
Registers: RA, RB or RC
Operation: Register <─ ACC
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x17XX |0x17 | LDR RA |- |
| 0x27XX |0x27 | LDR RB |- |
| 0x37XX |0x37 | LDR RC |- |
Note: 'X' means it doesn't matter.
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x1700 | LDR RA | Load into RA the content of ACC |
| 0x2700 | LDR RB | Load into RB the content of ACC |
| 0x3700 | LDR RC | Load into RC the content of ACC |
The MAddr/LAddr nibble is not used with this instruction, so it is left at 0.
The Instruction Word, for example, for LDR RA is coded as,
```asm
0x1700
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 0
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 7
└─────> Most significant Nibble => HiNB[b15:b12] = 1
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0001 0111 0000 0000
┆ ┆ ┆ └──> Operand = 0 (For this instruction, it doesn't matter)
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 7 (OPCode)
└─────────────────> HiNB = 1 (MICRO2_IN = 0, AMODE = 0, MOD = 1)
```
**CMP - Compare ACC**
Description: Performs the comparison between ACC with (Operand n, RA, RB or RAM).
The comparison is like a Subtraction, but it doesn't change the ACC.
The comparison result can be checked by Flags.
Operations:
ACC - Operand
ACC - Register
ACC - RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|----------------|
| 0x08Xn |0x08 | CMP ACC,n |CF,ZF |
| 0x18XX |0x18 | CMP ACC,RA |CF,ZF |
| 0x28XX |0x28 | CMP ACC,RB |CF,ZF |
| 0x38mn |0x38 | CMP ACC,@RAM |CF,ZF |
| 0x78XX |0x78 | CMP ACC,@R |CF,ZF |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|---------------|-|
| 0x0801 | CMP ACC,1 | Compare ACC with operand n |
| 0x1800 | CMP ACC,RA | Compare ACC with register RA |
| 0x2800 | CMP ACC,RB | Compare ACC with register RB |
| 0x38c3 | CMP ACC,@0xc3 | Compare ACC with RAM address. In this case, the RAM
address = RC:c:3 |
| 0x7800 | CMP ACC,@R | Compare ACC with RAM address. In this case, the RAM
address = RC:RB:RA |
The Instruction Word, for example, for CMP ACC,1 is coded as,
```asm
0x0801
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 1
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 8
└─────> Most significant Nibble => HiNB[b15:b12] = 0
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0000 1000 0000 0001
┆ ┆ ┆ └──> Operand = 1
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 8 (OPCode)
└─────────────────> HiNB = 0 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**OUTD - Send to OUTD output port**
Description: Sends the operand/Register or RAM value to the OUTD output port.
Operations:
OUTD <─ Operand
OUTD <─ ACC
OUTD <─ RA
OUTD <─ RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|----------------------|---------------|
| 0x09Xn |0x09 | OUTD n |- |
| 0x19XX |0x19 | OUTD ACC |- |
| 0x29XX |0x29 | OUTD RA |- |
| 0x39mn |0x39 | OUTD @RAM |- |
| 0x79XX |0x79 | OUTD @R |- |
Note:
The RAM address for @RAM is pointed by RC:MAddr:LAddr.
The RAM address for @R is pointed by RC:RB:RA.
The MAddr is represented by the letter "m".
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|-------------|-|
| 0x090b | OUTD 0xb | Sends the operand to the OUTD port |
| 0x1900 | OUTD ACC | Sends the ACC to the OUTD port. |
| 0x2900 | OUTD RA | Sends the RA to the OUTD port. |
| 0x39c3 | OUTD @0xc3 | Sends the content of RAM to the OUTD port. In this case, the
RAM address = RC:c:3|
| 0x7900 | OUTD @R | Sends the content of RAM to the OUTD port. In this case, the
RAM address = RC:RB:RA|
The Instruction Word, for example, for OUTD @R is coded as,
```asm
0x7900
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 0
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = 9
└─────> Most significant Nibble => HiNB[b15:b12] = 7
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0111 1001 0000 0000
┆ ┆ ┆ └──> Operand = 0 (For this instruction, it doesn't matter)
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = 9 (OPCode)
└─────────────────> HiNB = 7 (MICRO2_IN = 0, AMODE = 1, MOD = 3)
```
**STW - Store in RAM Memory**
Description: Stores the contents of the ACC in RAM.
Operation: RAM <─ ACC
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|---------------------|----------------|
| 0x0Amn |0x0A | STW @RAM,ACC |- |
| 0x4AXX |0x4A | STW @R,ACC |- |
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|---------------|-|
| 0x0A1f | STW @0x1f,ACC |Stores the contents of the ACC in RAM (address RC:1:f) |
| 0x4A00 | STW @R,ACC |Stores the contents of the ACC in RAM (address RC:RB:RA)|
The Instruction Word, for example, for STW @0x1f,ACC is coded as,
```asm
0x0A1f
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = f
┆┆└───> Second Nibble => MAddr[b7:b4] = 1
┆└────> Third Nibble => MICRO[b11:b8] = A
└─────> Most significant Nibble => HiNB[b15:b12] = 0
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0000 1010 0001 1111
┆ ┆ ┆ └──> Operand = f
┆ ┆ └───────> MAddr = 1
┆ └────────────> MICRO = A (OPCode)
└─────────────────> HiNB = 0 (MICRO2_IN = 0, AMODE = 0, MOD = 0)
```
**SUB - Subtract from accumulator**
Description: Subtracts from the accumulator the content of (Operand n, RA, RB or RAM) and stores the result in the accumulator.
Operation:
ACC <─ ACC - Operand
ACC <─ ACC - Register
ACC <─ ACC - RAM
| Instruction Word | ROMH | Instruction | Affected Flags |
|------------------|-----------------------|---------------------|----------------|
| 0x0BXn |0x0B | SUB ACC,n |CF,ZF |
| 0x1BXX |0x1B | SUB ACC,RA |CF,ZF |
| 0x2BXX |0x2B | SUB ACC,RB |CF,ZF |
| 0x3Bmn |0x3B | SUB ACC,@RAM |CF,ZF |
| 0x7BXX |0x7B | SUB ACC,@R |CF,ZF |
Examples:
| **Instruction Word** | **Instruction** | **Comment** |
|------------------|---------------|-|
| 0x0B0f | SUB ACC,0xf | Subtract from ACC the operand n and store the result in ACC |
| 0x1B00 | SUB ACC,RA | Subtract from ACC the Register RA and store the result in ACC |
| 0x2B00 | SUB ACC,RB | Subtract from ACC the Register RA and store the result in ACC |
| 0x3B9a | SUB ACC,@0x9a | Subtract from ACC the RAM address. In this case, the RAM
address = RC:9:a |
| 0x7B00 | SUB ACC,@R | Subtract from ACC the RAM address. In this case, the RAM
address = RC:RB:RA |
The Instruction Word, for example, for SUB ACC,RB is coded as,
```asm
0x2B00
┆┆┆└──> Least significant Nibble => Operand[b3:b0] = 0
┆┆└───> Second Nibble => MAddr[b7:b4] = 0
┆└────> Third Nibble => MICRO[b11:b8] = B
└─────> Most significant Nibble => HiNB[b15:b12] = 2
```
Also, the instruction word (in binary) to be manually programmed into MikroLeo using physical switches is,
```asm
0010 1011 0000 0000
┆ ┆ ┆ └──> Operand = 0 (For this instruction, it doesn't matter)
┆ ┆ └───────> MAddr = 0 (For this instruction, it doesn't matter)
┆ └────────────> MICRO = B (OPCode)
└─────────────────> HiNB = 2 (MICRO2_IN = 0, AMODE = 0, MOD = 2)
```
...
# Basic Documentation #
**- MikroLeo has four Registers**
`ACC` - Accumulator (4 bit) - Stores the result of logical and arithmetic operations. Moreover, ACC stores data that is read from or written to RAM.
`RA` - 4 bit General purpose Register (also used for addressing).
`RB` - 4 bit General purpose Register (also used for addressing).
`RC` - 4 bit Special purpose Register used for addressing.
**- Two Flags**
Flags can only be checked by conditional jump instructions (JPC and JPZ).
`CF` - Carry Flag - It is Set (CF=1) by ADD Instruction if it produces a carry or by SUB/CMP instruction if it results in a borrow.
`ZF` - Zero Flag - It is affected by operations that modify the contents of the ACC and by CMP instruction. It is Set (ZF=1) if the result of the last operation was zero.
Example of how CF and ZF are Set:
```asm
LDI ACC,1 ;Load the operand value into the ACC accumulator.
ADD ACC,0xF ;Performs the addition between the accumulator and the operand and stores the
;result in the accumulator.
```
This code does it,
```
0001
+ 1111
-------
1 0000
↓ ↓
CF ACC
As the value zero is written to ACC, ZF=1.
```
**- Addressing Modes**
*Immediate*
In immediate addressing, the operand (n) is contained in the lower nibble of the instruction (b3:b0), and it is denoted by Operand, LAddr or OPR.
Example 1:
```asm
LDI ACC,1 ;Load the operand value into the ACC accumulator.
```
Example 2:
```asm
LDI ACC,0xA
```
Example 3:
```asm
NAND ACC,0 ;Performs the NAND operation between the accumulator and the operand value and
;stores the result in the accumulator.
```
Example 4:
```asm
OUTA 0xF ;Sends the operand value to the OUTA output port.
```
Example 5:
```asm
CMP ACC,0 ;Performs the comparison between the accumulator and the operand.
```
Example 6:
```asm
SUB ACC,1 ;Performs the subtraction between the accumulator and the operand and stores
;the result in the accumulator.
```
Example 7:
```asm
ADD ACC,5 ;Performs the addition between the accumulator and the operand and stores the
;result in the accumulator.
```
*Register Direct*
In this mode, the operand must be one of the four registers (ACC, RC, RB, RA). Thus, the contents of the lower and medium nibble of the instruction (MAdrr, b7:b4 and LAddr, b3:b0) do not matter. Note that in the LDR instruction, the operand (ACC) is implied. LDR stands for load the Register Rx with ACC, being x={A,B,C}. In the LDA instruction, the operand must be one of the three registers (RC, RB, RA). LDA stands for load the accumulator with one of Rx Registers. Note that in register direct addressing mode, data can be read from or written to a register.
Example 1:
```asm
LDR RA ;Loads the value of the ACC accumulator into the RA register.
```
Example 2:
```asm
LDR RB ;Loads the value of the ACC accumulator into the RB register.
```
Example 3:
```asm
LDA RA ;Loads the value from the RA Register into the ACC accumulator.
```
Example 4:
```asm
LDA RC ;Loads the value from the RC Register into the accumulator ACC.
```
*Register Indirect + Absolute*
In this addressing mode, the `RC` Register points to the high address (b11:b8). The medium (MAddr) and low (LAddr) nibble of the instruction, point to the medium and low address, respectively.
The final address is composed by `RC:MAddr:LAddr`.
For example, if:
```
RC = 3
MAddr = 2
LAddr = 1
```
The address to be accessed is 321h.
In the MikroLeo python assembler, absolute addresses (`MAddr:LAddr`) are indicated by an @.
Example 1:
```asm
LDI RC,1 ;Loads the operand value into the RC Register.
OUTA @0xF4 ;Sends the contents of the RAM address pointed to by RC:MAddr:LAddr to output
;port A, in this case, the RAM address is RC:MAddr:LAddr = 1F4h.
```
Example 2:
```asm
LDI RC,3 ;Loads the operand value into the RC Register.
ADD ACC,@0xFC ;Sum the contents of the RAM address pointed to by RC:MAddr:LAddr with ACC
;and stores it in ACC. In this case, the RAM address is RC:MAddr:LAddr = 3FCh.
```
Example 3:
```asm
LDI RC,1 ;Loads the operand value into the RC Register.
JPI @0x23 ;Jumps to the specified label. In this case, the label address is
;RC:MAddr:LAddr = 123h.
```
Example 4:
```asm
LDI RC,2 ;Loads the operand value into the RC Register.
CMP ACC,0 ;Compares the contents of ACC with the operand. Is ACC equal to 0?
JPZ @0x34 ;Jumps to the specified label if ZF=1 (ACC = 0). In this case, the label
;address is PCH:MAddr:LAddr = PCH:34h. JPZ does not affect PCH.
```
Example 5:
```asm
LOOP:
LDI RC,3 ;Loads the operand value into the RC Register.
STW @0x21,ACC ;Stores the contents of the accumulator in the RAM address pointed by
;RC:MAddr:LAddr, in this case, the RAM address is RC:MAddr:LAddr = 321h.
LDI RC,>LOOP ;Gets the address of the label, as this code changes the contents of the
;Register RC.
JPI LOOP ;Jumps to the specified label.
```
Example 6:
```asm
LOOP:
LDI RC,3 ;Loads the operand value into the RC Register.
LDW ACC,@0x21 ;Loads the contents of the RAM address pointed by RC:MAddr:LAddr in the
;accumulator, in this case, the RAM address is RC:MAddr:LAddr = 321h.
LDI RC,>LOOP ;Gets the address of the label, as this code changes the contents of the
;Register RC.
JPI LOOP
```
Example 7:
```asm
LOOP:
LDI RC,4 ;Loads the operand value into the RC Register.
CMP ACC,@0x32 ;Compares the contents of ACC with the contents of the RAM address
;pointed by RC in this case, the RAM address is RC:MAddr:LAddr = 432h.
;Is ACC equal to @432h?
JPZ LOOP ;Jumps to the specified label if ZF=1 (ACC = @432h).
```
*Register Indirect*
In this addressing mode, the `RC` Register points to the high address (b11:b8). Likewise, the `RB` Register points to the medium Address (MA) while the `RA` Register points to the low Address (LA). Note that the contents of the lower and medium nibble of the instruction (MAddr, b7:b4 and LAddr, b3:b0) do not matter.
The final address is composed by `RC:RB:RA`.
For example, if:
```Thus, the contents of the lower and medium nibble of the instruction (b7:b4, b3:b0) do
not matter.
RC = 3
RB = 2
RA = 1
```
The address to be accessed is 321h.
In MikroLeo's python assembler, indirect register addresses (`RC`:`RB`:`RA`) are indicated by an @R.
Example 1:
```asm
LDI RC,1 ;Loads the operand value into the RC Register.
LDI RB,0xF
LDI RA,4
OUTA @R ;Sends the contents of the RAM address pointed to by RC:RB:RA to output
;port A,
;in this case, the RAM address is RC:RB:RA = 1F4h.
```
Example 2:
```asm
LDI RC,3 ;Loads the operand value into the RC Register.
LDI RB,0xF
LDI RA,0xC
ADD ACC,@R ;Sum the contents of the RAM address pointed to by RC:RB:RA with ACC
;and stores it in ACC. In this case, the RAM address is RC:RB:RA = 3FCh.
```
Example 3:
```asm
LDI RC,1 ;Loads the operand value into the RC Register.
LDI RB,2
LDI RA,3
JPI @R ;Jumps to the specified label. In this case, the label address is
;RC:RB:RA = 123h.
```
Example 4:
```asm
LDI RC,2 ;Loads the operand value into the RC Register.
LDI RB,3
LDI RA,4
CMP ACC,0 ;Compares the contents of ACC with the operand. Is ACC equal to 0?
JPZ @R ;Jumps to the specified label if ZF=1 (ACC = 0). In this case, the
;label address is PCH:RB:RA = PCH:34h. JPZ does not affect PCH.
```
Example 5:
```asm
LOOP:
LDI RC,3 ;Loads the operand value into the RC Register.
LDI RB,2
LDI RA,1
STW @R,ACC ;Stores the contents of the accumulator in the RAM address pointed by
;RC:RB:RA, in this case, the RAM address is RC:RB:RA = 321h.
LDI RC,>LOOP ;Gets the address of the label, as this code changes the contents of
;the Register RC.
JPI LOOP ;Jumps to the specified label.
```
Example 6:
```asm
LOOP:
LDI RC,3 ;Loads the operand value into the RC Register.
LDI RB,2
LDI RA,1
LDW ACC,@R ;Loads the contents of the RAM address pointed by RC:RB:RA in the
;accumulator, in this case, the RAM address is RC:RB:RA = 321h.
LDI RC,>LOOP ;Gets the address of the label, as this code changes the contents of
;the Register RC.
JPI LOOP
```
Example 7:
```asm
LOOP:
LDI RC,4 ;Loads the operand value into the RC Register.
LDI RB,3
LDI RA,2
CMP ACC,@R ;Compares the contents of ACC with the contents of the RAM address
;pointed by RC in this case, the RAM address is RC:RB:RA = 432h.
;Is ACC equal to @432h?
JPZ LOOP ;Jumps to the specified label if ZF=1 (ACC = @432h).
```
# Assembler Compiler #
Released!
See examples how to use...
# How to transfer compiled program to MikroLeo #
[Download documentation (pdf file)](https://github.com/edson-acordi/4bit-microcomputer/raw/master/Docs/How%20to%20transfer%20a%20compiled%20program%20to%20MikroLeo.pdf "download")
# Emulator #
In progress...🚧
# Demo #
MikroLeo in action!
A simple program to make a LED sequencer using the output ports.
A simple program to initialize an LCD.
# Building your own MikroLeo #
...:soon:
# Contribution guidelines #
...:soon:
# Pictures #
Simulation of the MikroLeo circuit (Made with "Digital"):
[Digital](https://github.com/hneemann/Digital) is free, open source and cross-platform software with a nice interface for digital logic design and circuit simulation.
Breadboard:
PCB (KiCad 3D viewer):
To carry out the project, the [KiCad](https://www.kicad.org/) software was used, an excellent and powerful free and open-source tool for printed circuit board (PCB) designers.
Size: 295.9mm x 196.9mm
A simple seven-segment display interface (the PCB has a layout thought for educational purposes, that's why it got big),
Size: 88.65mm x 141.mm
PCB Prototype:
-------------------------------------------
# Development stages #
- [x] - Bibliographic research
- [x] - Architecture definition
- [x] - Circuit design
- [x] - Circuit simulation
- [x] - Prototype assembly on breadboard
- [x] - Printed circuit board design
- [x] - Prototype assembly on PCB
- [ ] - Final Tests
# History and Motivation #
Since the time I took an 8086 assembly language programming course and took digital electronics and microprocessors classes in college, this project has been something I've always wanted to do. I'm fascinated by electronics, computers and programming!
The project started in 2020, and the first usable version was completed on April 20, 2020.
Initially, the development of the project used the [Logisim-Evolution](https://github.com/logisim-evolution/logisim-evolution), and later it was migrated to the [Digital](https://github.com/hneemann/Digital).
#### Some sources of inspiration can be seen at:
http://www.sinaptec.alomar.com.ar/2018/03/computadora-de-4-bits-capitulo-1.html
https://www.bigmessowires.com/nibbler/
https://gigatron.io/
https://eater.net/
https://apollo181.wixsite.com/apollo181/specification
https://www.megaprocessor.com/
http://www.mycpu.eu/
https://minnie.tuhs.org/Programs/CrazySmallCPU/index.html
# Dedication #
I dedicate this project to my beloved son, Leonardo Pimentel Acordi.
# Acknowledgements #
### The authors would like to thank:
- The IFPR (Instituto Federal do Paraná), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and Fundação Araucária for the partial funding and support for this project.
- The RENESAS (https://www.renesas.com/br/en) for sending me memory samples for tests with MikroLeo.
- All people from the Github community and externals who support this project.
# Sponsor #
Starting with revision 1.02A (which will be finalized soon) MikroLeo has gained a sponsor for the printed circuit board, the PCBWAY company, a serious company that produces high-quality PCBs.
https://www.pcbway.com/
# Authors #
>Edson Junior Acordi
Matheus Fernando Tasso
Carlos Daniel de Souza Nunes
# License #
**Hardware:** Licensed under CERN-OHL-S v2 or any later version
https://ohwr.org/cern_ohl_s_v2.txt
**Software:** Licensed under GNU GPL v3
https://www.gnu.org/licenses/gpl-3.0.txt
**Documentation:** Licensed under CC BY-SA 4.0
https://creativecommons.org/licenses/by-sa/4.0/
>***Note:***
As this project is intended for educational purposes, I have decided to use the CERN-OHL-S license for hardware to ensure that it is always free, contributing, promoting and disseminating the essential knowledge. As such, all hardware derived from it will also be open source!
Likewise, for the software, the GNU GPL license was used.
## Contact ##
***Note:*** If you have any questions, please consider opening a discussion first, as your question may be helpful to others. If you want to report a bug, please open an issue.
You can also contact me via email: [[email protected]](mailto:[email protected])
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