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https://github.com/hzeller/trs80-100-schematic

A transcript of the TRS80 Model 100 schematic
https://github.com/hzeller/trs80-100-schematic

schematics tandy-trs80-model100 trs-80 trs-80model100 vintage-computers

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A transcript of the TRS80 Model 100 schematic

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README 

        
Schematic Transcript of TRS-80 Model 100

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[![CC BY-SA 4.0][cc-by-sa-shield]][cc-by-sa]



This is a transcript of the original schematic found in the TRS-80 Model 100

manual into a machine-readable and libre license format using KiCAD (7.0).



This transcript is based on various scans to minimize read errors



  * https://tim.id.au/trs-80-model-100.pdf

  * https://archive.org/details/tandy_100_schematics/page/n11/mode/2up

  * https://archive.org/details/trs-80-model-100-main-pcb-schematic-from-tech-ref-manual  (this is the highest quality, found it after finished the transcript,

  but excellent as proof-read reference)



The format is in KiCAD eeschema format; for convenience, a generated PDF

has been included in this repository.










Browse interactively

with the excellent KiCanvas viewer in the browser.



## Status



The main-board schematic is complete (the LCD one has not started yet).

All values in the BOM have been cross-checked with the BOM printed

service manual and are matching.

The schematic passes ERC with zero warnings and errors.



A fine-combed proof-reading and comparison between original and transcript

for all nets being connected correctly has yet to be done.



## Minimal layout deviation



This transcript in KiCAD attempts to preserve the high-level original layout

as much as possible to easily navigate and compare between the original and the

transcript. This means as well that some schematic symbols exists in multiple

different versions for the same chip to accommodate the same pin-sequence found

in the original schematic which were chosen to simplify the layout (for

instance, there are versions for 40H244 for M15, M21, M23, and M32).



Some parts have been rearranged to improve readability and make areas less

visually crowded.



The reset circuit have been arranged in a way that the functionality is

easier to read than in the original schematic (mostly making sure positive

is up and GND is down, and voltage dividers are not 'around corners').



Readability improvements have been done in the address demultiplexing

section to more easily see the `AD[0..7]` bus being buffered to the AD-bus and

latched to the lower half of the address bus.



A `RDWR` signal and its buffered counterpart `RDWR*` have been introduced.

In the original schematic, the former was not named but generated to feed

the `ENABLE` for the LCD. The `RDWR*` signal existed but was named `Ⓐ*` in

the original schematic which was not a very useful name.



Now, these signals are generated close to the 'bus buffer signal' section, the

`RDWR` section is used as a named signal in the LCD input (which also makes the

section near the LCD connector less crowded). As a result, the buffer

section is also less crowded by using a block symbol as M20 instead of

multiple separate buffer symbols (note, the `RESET_OUT` signal has been

moved to the right of the 80C85 symbol for that).



The RAM and ROM chips in the original hand-drawn schematic in a 'stacked'

format. The individual chips are made explicit in the transcript.



All component designators have been preserved and all pin-assignments

of components are the same as in the original schematic.

(Only exception: the pinouts of the resistor networks have not been arranged

yet; but pin numbers are hidden, so it would not make a difference unless a PCB

is made).



Different busses have been color-coded:



  * Green: unbuffered AD bus from the CPU; named with underscore `_AD[0..7]`

  * Magenta: buffered AD bus `AD[0..7]`

  * Orange: Address bus `A[0..15]` (which includes the demultiplexed `A[0..7]`).

  * Blue: Periphery IO lines from 81C55: `PA[0..7]`, `PB[0..1]`.



For labels with a meaning across the schematic that are not part of

a bus, mostly global labels have been used, mostly because they stand out

more nicely than simple labels.



## Designators



Some designators have been deduced by cross-referencing the schematic

and BOM. These need to be verified on the actual PCB.



The 10nF capacitor in the switching power supply section does not have a

designator in the schematic. The C62 designator was extracted from the BOM,

as this designator was the only missing and also had the correct 10nF value

(to be verified on PCB).



The base transistor to T4 is a 10k value with no designator in the schematic.

This is likely R33, but not confirmed yet.



The resistor discharging C78 via T25 has neither a designator nor value in

the schematic. This could be R162 with 100 Ohm. To be confirmed.



### Missing designators



There are a few missing designator numbers, but these have also been missing

in the original BOM. So for completeness, following designators do *not* exist:



  * D3, D19, D25, D26

  * C51, C68, C93, C95, C96

  * R69, R100, R117, R129, R130, R133, R143, R147, R148, R155, R163..R169



### Fixes to the original schematic



  * C37 is shown as 47n, while the BOM and PCB says 100n.

  * The keyboard has a wrong assignment of the cursor keys; they are

    in different rows in the key-matrix than they actually are. Fixed

    in this transcript as result from actual measurement.

  * Missing designators R33, R162 and C62 have been added.

  * Fixed SW1 (Originate/Answer) inconsistent lever position.



## TODO



  * Thorough comb-through to make sure there are no mistakes and

    confirm R33 (Base-resistor for T4?), R162 (reset circuit?) (look at PCB).

  * Fill in details (voltage, tolerance, original part names (many have original

    Radio Shack part-numbers), datasheets if possible) for each component

    from the original BOM.

  * Add footprints to all components that they reflect exactly the original

    components.

  * Add Makefile to create schematic PDF and BOM from eeschema file.



## BUGS



If you see mistakes, please file them in the issue tracker;

https://github.com/hzeller/trs80-100-schematic



## Transcript License CC-BY-SA



The original schematic is copyright of the respective owner (probably Kyocera).



This editable transcript in KiCAD format is licensed by me, Henner Zeller,

under Creative Commons Attribution-ShareAlike CC-BY-SA 4.0 license.



[cc-by-sa]: http://creativecommons.org/licenses/by-sa/4.0/

[cc-by-sa-shield]: https://img.shields.io/badge/License-CC%20BY--SA%204.0-lightgrey.svg