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Add detailed troubleshooting commands

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Tom Nisbet 2020-07-17 11:17:56 -04:00
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docs/troubleshooting.md
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@ -77,3 +77,90 @@ Writing the unlock code to disable Software Write Protect mode.
#cd
```
## Troubleshooting
If the programmer seems to be working, but 28C256 EEPROMs cannot be written, the problem
may simply be a locked chip. Some chips have been received with the Software Data
Protection (SDP) enabled, even though the data sheet states that it should be disabled
from the factory. If the chip does not write (try the Zap command in the TommyPROM code),
then try an Unlock command and then retry the write.
If the programmer is not working, the most common problem is a simple wiring error. The
hardware verify sketch can help to find missing or crossed connections.
The hardware has three sections: an 8-bit read-write data bus connected to the target
PROM's data line, a set of write-only address lines generated by shift registers and
connected to the target PROM's address lines, and a set of write-only control lines from
the Arduino that toggle the PROM's output enable and write lines.
The first step in general testing it to remove the target chip and then toggle single
lines from the Arduino. The result should be measured at the target PROM footprint, not
at the Arduino. To fully test, use a multimeter to verify that the lines that should be
active are active and that any other lines are not.
### Testing the data bus
Issue a set of Data commands from the Hardware Verify sketch and measure EACH data line at
the PROM footprint. **If the expected result is "D0 HIGH", verify not only that D0 reads
HIGH, but that all of the other lines read LOW.**
Data test commands
|Command|Result|
|:--- |:--- |
|D0 |All data lines LOW|
|D1 |D0 HIGH|
|D2 |D1 HIGH|
|D4 |D2 HIGH|
|D8 |D3 HIGH|
|D10 |D4 HIGH|
|D20 |D5 HIGH|
|D40 |D6 HIGH|
|D80 |D7 HIGH|
|Dff |all data lines HIGH|
### Testing the address lines
As with the data tests above, verify not only the line with the expected result, but all
other address lines as well.
|Command|Result|
|:--- |:--- |
|A0 |All address lines LOW|
|A1 |A0 HIGH|
|A2 |A1 HIGH|
|A4 |A2 HIGH|
|A8 |A3 HIGH|
|A10 |A4 HIGH|
|A20 |A5 HIGH|
|A40 |A6 HIGH|
|A80 |A7 HIGH|
|A100 |A8 HIGH|
|A200 |A9 HIGH|
|A400 |A10 HIGH|
|A800 |A11 HIGH|
|A1000 |A12 HIGH|
|A2000 |A13 HIGH|
|A4000 |A14 HIGH|
|A7fff |all address lines HIGH|
### Testing the control lines
The PROM control lines are active LOW, so an enable command will set the corresponding
control line LOW and a disable will set it HIGH. Try the commands in the following table.
Note that they should be done in the order listed, because a test command on one control
line will not change the state of any of the other lines.
To begin, issue the following commands: D0, A0, Cd, Od, Wd. Note that the Od command is
the letter 'O', not the number zero. All three control lines should read HIGH after these
commands are complete.
|Command|Result|
|:--- |:--- |
|Ce | Chip Enable (CE) LOW, others HIGH|
|Cd | CE, OE, WE all HIGH|
|Oe | Output Enable (OE) LOW, others HIGH|
|Cd | CE, OE, WE all HIGH|
|We | Write Enable (WE) LOW, others HIGH|
|Wd | CE, OE, WE all HIGH|