(Topic ID: 252795)

What am I doing wrong with EPROM


By jgadzia

13 days ago



Topic Stats

  • 19 posts
  • 4 Pinsiders participating
  • Latest reply 8 days ago by Tuukka
  • Topic is favorited by 1 Pinsider

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#1 13 days ago

Ok i have been trying to burn leons rom, and i tried the newest version and recently tried the older version. I can get neither of them to work appropriately. I have included a video of start to stop, hoping someone can figure out what i am doing wrong. I would appreciate any help.
i did notice when i look at the buffer, it appears to be full of FF's through most of the buffer, which seems that it is blank?

#2 13 days ago

The Leon system 11/data east chip from pinwiki anyway is supplied on a 27512 chip. It looks like it's just a doubled up 27256 image though, I split it in half and both halves verified with each other.

Looking at the code split in pinmame, there are 3 bytes starting at offset $257 that are 00 00 00 - this is an illegal opcode. Now, pinmame just skips right over these because it might not be 100% cpu accurate, or a later revision cpu fixes this error (illegal opcodes usually do something unpredictable in a microprocessor).

You can change those 3 00 bytes in your editor to be "01 01 01" which is the 6800/02/08 opcode for "nop" (no operation) and see if it works that way.

#3 13 days ago

i am not seeing what you are seeing. when i open this file in a hex editor this is what i see. this appears identical to what i see in the buffer on the eprom burning software.

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#4 13 days ago
Quoted from jgadzia:

Ok i have been trying to burn leons rom, and i tried the newest version and recently tried the older version. I can get neither of them to work appropriately. I have included a video of start to stop, hoping someone can figure out what i am doing wrong. I would appreciate any help.
i did notice when i look at the buffer, it appears to be full of FF's through most of the buffer, which seems that it is blank?

What is the 27256 Leon checksum?

#5 13 days ago

Remove J5 and connect J4 to run a 27256 in C5
retest chip

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#6 13 days ago
Quoted from PINTEC:

What is the 27256 Leon checksum?

007DAB2C

#7 13 days ago

ok only have jumpers in J3 and J4. Verified continuity.

Erased EProms. verified they were blank. Rewrote Eprom. Verified Write. removed Eprom and re-read it get the same checksum. put EProm in board and get the same thing. +5v and Pia light stay lit.

#8 13 days ago
Quoted from jgadzia:

ok only have jumpers in J3 and J4. Verified continuity.
Erased EProms. verified they were blank. Rewrote Eprom. Verified Write. removed Eprom and re-read it get the same checksum. put EProm in board and get the same thing. +5v and Pia light stay lit.

What is your email I'll send the 27256 Leons I have confirmed working.

#9 12 days ago
Quoted from jgadzia:

i am not seeing what you are seeing. when i open this file in a hex editor this is what i see. this appears identical to what i see in the buffer on the eprom burning software.

Looks like that's a different version of the chip then what I downloaded from pinwiki. Pinwiki's said it was version 5, and your offset is the text part (which is never executed).

Quoted from PINTEC:

What is your email I'll send the 27256 Leons I have confirmed working.

Pintec can you compare what you have to what is on pinwiki - seems like the pinwiki one might be wrong as there shouldn't be 3 illegal opcodes in the middle of the test. The pinwiki is a 512 image but it's just a doubled up 256.

#10 11 days ago

ok i burned the smaller leons rom and put it in the non-working board, and I got the pia flashing (after i changed the jumpers at J4 and J5). put it back in the supposedly working board and still couldnt get the pia to flash. I went ahead and tested the non-working board and found that the PIA for the DMD was bad and replaced it. Stuck Leons rom back in and tested it and everything seems to be working ok. So now i am left with the board that i still cant get leons rom to run, went a little further into the wiki. It says that i should get 4 volts at pin 40, and i am only getting 0.19 volts. but i checked the working board and i was getting the exact same voltage there, so not sure if that is a problem or not. I took my oscilloscope and checked the vma, the clock and the e signal. I think the problem might be the vma. here is the pic of my vma signal on the oscilloscope. If i trace that back to 7E is there some test that i can do there to see if it goes back further to 7c or 7D?

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#11 10 days ago

For a more meaningful display, set your scope to 2V/div and 500ns or 1us/div, this is a 5 volt and 1MHz system.

#12 10 days ago
Quoted from Tuukka:

For a more meaningful display, set your scope to 2V/div and 500ns or 1us/div, this is a 5 volt and 1MHz system.

i will do that when i get home tonight, but this was the only setting where i felt i could see anything, everything else looked like a line.

#13 10 days ago

Start with the clock or E signal at 2V/1us /div and you should see a more or less perfect square wave. Adjust trigger level if necessary until the waveform "freezes" in display.

Then, you can move the scope probe to other signals but don't touch the scope settings. If you see a solid line near 0 or 5 volts that means the signal stays at logic 0 or 1, or doesn't change very often. Most, if not all, logic signals in game CPU do change states continuously so a solid 0 or 1 is usually a sign of problem. For signals changing only occasionally, such as IRQ, you need to tinker with scopes triggering settings, but anyway if you observe the clock and E signals and activity on data/address bus the CPU is definitely running. Next to check would be the /CE inputs of ROM and RAM, those should be periodically pulsing low.

#14 10 days ago

first pic is pin 39 clock
second pic is pin 37 e signal
third pic is vma which i am guessing is bad

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#15 10 days ago

Yes, your clock and E are fine but there is definitely something wrong with VMA, it should be mostly high. Try another 6802.

Edit: also might be possible that the CPU has problems reading ROM and gets a WAI instruction and then halts waiting for interrupt with VMA low. Anyway, testing with another CPU chip will help.

#16 9 days ago

can someone explain what the vma stands for and what it does?

#17 9 days ago

VMA stands for valid memory address. CPU sets VMA high when it has set a memory address on the bus, for reading or writing memory. So whenever the CPU is running a program the VMA should show activity.

The CPU can be set to a state in which it does nothing, but waits for an interrupt (a low in IRQ or NMI pins) and in that state it does not assert VMA.

#18 8 days ago
Quoted from Tuukka:

VMA stands for valid memory address. CPU sets VMA high when it has set a memory address on the bus, for reading or writing memory. So whenever the CPU is running a program the VMA should show activity.
The CPU can be set to a state in which it does nothing, but waits for an interrupt (a low in IRQ or NMI pins) and in that state it does not assert VMA.

so if the cpu is sending out the vma and i am measuring no voltage at pin 5, does that mean the cpu is bad or the chip at 7e?

#19 8 days ago

I would try with another CPU first.

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