TommyPROM/docs/troubleshooting.md

title	description	has_children	nav_order
Troubleshooting	Troubleshooting TommyPROM hardware	false	50

Hardware Verifier Tool

A Hardware verification Arduino sketch is provided to assist with troubleshooting. Loading this sketch onto the TommyPROM hardware allows access to individual control lines from the Arduino to verify that the hardware was assembled correctly.

The verifier sketch can be used without a chip installed to scope out address and data lines. It also offers low-level control when the chip is installed.

THIS TOOL USES DIRECT PORT ACCESS ON THE ARDUINO. CHECK TO MAKE SURE IT IS COMPATIBLE WITH YOUR BOARD BEFORE USING. It will work correctly on the Uno, Nano, and Boarduino. It WILL NOT WORK on the Micro.

Note that the commands write to the individual 28C control lines with some exceptions to protect the chip and the host Arduino:

• When the O command is used to enable chip output, the Arduino data bus is set to INPUT
• When the D command is used to write data from the Arduino, the chip output is disabled
• The R command sets the output enable (OE) on the chip, but not the chip enable (CE)
• The L and U commands reset CE, OE, and WE back to disabled on completion and change the data and address

The session below shows how a write fails to a locked chip and then succeeds once the chip is unlocked.

Hardware Verifier - 28C series EEPROM

Valid commands are:
  Axxxx         - Set Address bus to xxxx
  Dxx           - Set Data bus to xx
  Cs            - Set Chip enable to state (e=enable, d=disable)
  Os            - Set Output enable to state (e=enable, d=disable)
  Ws            - Set Write enable to state (e=enable, d=disable)
  R             - Read and print the value on the data bus
  L             - Send Lock sequence to enable device Software Data Protection
  U             - Send Unlock sequence to disable device Software Data Protection

#l
Writing the lock code to enable Software Write Protect mode.

#a0000

#ce

#r
22

#d55

#we

#wd

#r
22

#u
Writing the unlock code to disable Software Write Protect mode.

#d33

#we

#wd

#r
33

#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.

Note that the Dx and Ax commands can be a bit confusing. The command D5 means "set the value 05 HEX on the eight data lines". It does not specifically refer to the D₅ data pin on the ROM or the D5 pin on the Arduino. In the example above, 05 HEX is the same as 00000101 BINARY. This would set the ROM D₀ and D₂ pins HIGH and the other six pins would be LOW.

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
Od	CE, OE, WE all HIGH
We	Write Enable (WE) LOW, others HIGH
Wd	CE, OE, WE all HIGH