microcontroller ROM copy trouble ?

I have a working (ie. tested) microcontroller board uses a (Philips MAB-8031-AH-12p) MCU a 8051 variant, maybe romless ? with a (NEC 23256AC) ROM chip.

i removed the ROM chip (NEC D23256AC) and copied it using a ROM programmer, then i programmed that ROM image onto a (ST M27C256B) EPROM

i put the new ROM (ST) onto the microcontroller board and i

t does **NOT** work ... a no go. i removed the ROM (ST) and put the ROM (NEC) back and works like a charm... no problems

i download ROM images from both (NEC) and (ST) and compare in file compare program which declares them as exactly the same ?????

HELP please?? any ideas what is going on here.

the only funny thing about the microboard (that i know) is that the ROM memory socket has (pin1) tied to (pin 27) that is Addr15 (pin 1) and Addr 14 (pin 27) ??? do not know why ????

thanks for any help i am stuck again, robb

Reply to
robb
Loading thread data ...

One possibility is that the speed grade of the EPROM is slower than that of the original ROM chip. There should be a couple of digits after a dash on each chip, like -12 or -70. What are they?

Reply to
Rich Webb

ROM

M27C256B)

than

digits

Thanks for reply Rich,

I have a variety of ROMs i have tested

i have a set of uv eraseable and OTP both of the 10 12 15 variety (ie. 100/120/150 ns)

the original equipment is from 1987-89 ...so i do not think it is terribly fast, the clock is 12 Mhz. I could not locate an exact datasheet for the (NEC D23256AC 016 8437k9) but the one 23256ac i did find was rated at 150 ns i tried to match or better that number.

faster than spec chip is OK i presume ?

the 8031 processor has a Time of Address Valid to Instruction Read Valid of 300 ns (max value)

do any of these numbers sound close (bad) ?

****And more info**** ... There is no funny business with 8031 processor because i was able to sub in a **brand new/ not used ** Atmel 8031 processor in place of the original 8031 and worked great ???? with the original ROM if that means anything

Thanks again for your help i am really stuck here and wondering if there is some security measure installed on the original ROM but that just seems unlikely ???? unless that funny stuff with the Address line has something to do with it ???

but my reconing on that is.... if i have the same raw image on the two ROM chips then the processor sould see no difference in the data it reads from either chip using the same interface to those two chips ? yes /no /maybe ?

Thanks again for help Rich, robb

Reply to
robb

[condense]

Thinking there might be some MCU 8031 funny business/security i swapped a ** brand new / not used** (Atmel 80C31x2-UM) in place of original 8031 and works like a charm...

........with the **Original ROM ONLY ***

could really use some ideas , i am stumped, robb

Reply to
robb

My guess is that here is a subtle pin difference between the eproms... speed is definitely NOT an issue.

Reply to
TT_Man

It *looks* like the memory chips are faster than the processor, so that may not be the issue. The original was probably 160 ns.

The note at the back of the TMM23256P data sheet (I'm guessing that is the one that you also found) does reference a required initialization sequence. If you can, scope out which of the two sequences are used and perhaps determine whether that sequence is disturbing the alternate chip in some way.

--
Rich Webb     Norfolk, VA
Reply to
Rich Webb

--
If the same image is programmed into both devices and they both have
identical pinouts, then I\'d look at I/O level differences.
Reply to
John Fields

You didn't read what he wrote did you ?

He has an *external* ROM.

Graham

Reply to
Eeyore

Been there (or somewhere similar). Is Vpp connected? (to Vcc?). In the case I saw EPROM's programmed & verified (in programmer), but the output disappeared almost instantly in the real circuit where Vpp wasn't connected (to Vcc). (2716's).

Reply to
gqrxzy8974

if memory serves me right the 27... is a progamable chip and you apply a programming voltage to a certain pin. To read that chip you must change "that" pin to hi or low. I got on datasheets here.

Reply to
Ryan Weihl

find

so

that

initialization

used

alternate

Thanks Rich, I scoped the working chip in operation and i saw wave forms i was not expecting ? the (pin 1) was particulalry different /peculiar.

i will ooku pthe sequence next and see if i can decipher what i see. thanks again , robb

Reply to
robb

What is pin 1 of the ROM connected to ? It may simply be floating.

Try tying it low.

Graham

Reply to
Eeyore

--
You didn\'t understand what I wrote, did you?
Reply to
John Fields

ROM

M27C256B)

Vcc?).

programmer),

well oddly on this board the (pin 1) is hardwired to (pin 27)

for the original chip that is ( NC to Addr 14) on the **new**

27c256 that would be (Vpp to Addr 14)

so i **tried** insert new 27C256 into socket with (pin 1) not making contact(bend pin and slide to outside of socket) then attach micro-jumper hooks from (pin 1) to Vcc

and this did not have any effect ??

so now i am wondeing if i am even reading the original Chip correctly it is ***NOT*** directly supported /mentioned in my ROM reader but it has similar equivalents by my judgement but the data does not look like it is thr 8051 processor instructions as i would expect.

thanks for help , robb

Reply to
robb

You could try running the ROM contents through a disassembler. That should tell you if it's junk or not.

Graham

Reply to
Eeyore

robb wrote: [snip...snip...]

*Reading* is (nearly) universal for memory chips with a standard pinout. *Programming* is often vendor-specific and not well documented in end-user data sheets.

Have you tried running the object code through a disassembler? I've used D52, which is available at

formatting link

--
Rich Webb     Norfolk, VA
Reply to
Rich Webb

That doesn't sound odd as pin 1 would be A15 on the next size up ROM.

OK, so that's not the problem.

Have you looked at a hex dump of the ROM? Perhaps it didn't really enabel the ROM when reading it and you "read" all FF or something like it from the original ROM and it programmed your new EPROM with that.

Mask ROMs can have additional chip selects (if pins are available) and these can be (mask programmed) to select on high or low. There may or may not be an OE (possibly just the chip select(s)).

It's a 28 pin chip and has to have gnd, Vcc, 8 data,

15 address so that leaves 3 pins. The eprom has CE, OE, and Vpp; the ROM might have 3 more chip selects or some number of chip selects plus OE?

It sounds solvable...

Reply to
gqrxzy8974

find

Instruction

so

that

initialization

used

alternate

uhmm.... any ideas on how to scope an initializing sequence ? it's to fast or my adjusting or triggering is a problem ???

robb

Reply to
robb

Honestly, I just skimmed the replies, and don't have the time to get into great detail about what might be wrong....

However, if I recall correctly, parallel EPROMs used to have "Signature Bytes". In the old days, that's how a programmer "knew" what programming voltage / algorithm to use....

Could be the 8031 code is reading this, before allowing normal operation. (Wild ass guess, btw) Or, perhaps more likely, your programmer isn't really programming the new EPROM and its just lying to you.??

Hope you figure it out. Good luck.

-mpm

Reply to
mpm

Vpp needs to be held at Vcc for reading. If it floats you will get garbage results.

Reply to
budgie

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.