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

robb wrote:
> 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.

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?

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:13n80kei7it4gef@corp.supernews.com...
> robb wrote:
> > 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
> > it does **NOT** work ... a no go.
> >
> > HELP please?? any ideas what is going on here.
>
> 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?
>

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

>> 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) ?

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

robb wrote:
>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) ?

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

On Thu, 27 Dec 2007 14:28:49 -0500, "robb" <some@where.on.net>
wrote:

>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,

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


--
JF

John Fields wrote:

> If the same image is programmed into both devices

You didn't read what he wrote did you ?

He has an *external* ROM.

Graham

On Dec 27, 11:28 am, "robb" <s...@where.on.net> wrote:
> I have a working (ie. tested)microcontrollerboard 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 themicrocontrollerboard 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

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).

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:13n8d1namek1132@corp.supernews.com...
> robb wrote:
> >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.
>
> 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.
>

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

robb wrote:

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

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

Try tying it low.

Graham

On Fri, 28 Dec 2007 04:14:21 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>John Fields wrote:
>
>> If the same image is programmed into both devices
>
>You didn't read what he wrote did you ?
>
>He has an *external* ROM.

---
You didn't understand what I wrote, did you?


--
JF

<gqrxzy8974@ftml.net> wrote in message
news:4f33ad0b-493c-4adf-8d07-de0cebafbf62@e6g2000prf.googlegroups.com...
> On Dec 27, 11:28 am, "robb" <s...@where.on.net> wrote:
> > I have a working (ie. tested)microcontrollerboard 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 themicrocontrollerboard and
> > t does **NOT** work ... a no go.
>
> 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).
>

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

robb wrote:

> 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.

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

Graham

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

*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 http://www.8052.com.

--
Rich Webb Norfolk, VA

> 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)

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

> 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 ??

OK, so that's not the problem.

> 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.

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...

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:13n8d1namek1132@corp.supernews.com...
> robb wrote:
> >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) ?
>
> 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

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

robb

On Dec 27, 2:28=EF=BF=BDpm, "robb" <s...@where.on.net> wrote:

> thanks for any help i =EF=BF=BDam stuck again,
> 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

On Fri, 28 Dec 2007 12:43:12 -0500, "robb" <some@where.on.net> wrote:

>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.

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

<gqrxzy8974@ftml.net> wrote in message
news:e16006dc-aebf-4d57-8a46-8a1e9409e066@e23g2000prf.googlegroups.com...
> > 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)
>
> That doesn't sound odd as pin 1 would be A15 on the next
> size up ROM.
>
i think i may not be clear ?
i am saying pin 1 and pin 27 of the memory chip are connected on
the controller board so that would cause special consideration if
one wanted to use a 27c512 ?

>
> > 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 ??
>
> OK, so that's not the problem.
>
> > 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.
>
> 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.
>

close , it is a series of sections of 64 duplicate bytes
followed by another section of 64 duplicate bytes..... all the
waty to the end

each section of byte values is different and i get the exact
same series for each successive chip reading attempts.

unless i choose a different chip size like 27c128 then the series
of byte duplicates changes. where the first set maybe 7A in place
of the 02

here is a clip from begining of my read

:020000040000FA
:1000000002020202020202020202020202020202D0
:1000100002020202020202020202020202020202C0
:1000200002020202020202020202020202020202B0
:1000300002020202020202020202020202020202A0
:100040000202020202020202020202020202020290
:100050000202020202020202020202020202020280
:100060000202020202020202020202020202020270
:100070000202020202020202020202020202020260
:10008000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9E0
:10009000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D0
:1000A000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9C0
:1000B000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9B0
:1000C000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9A0
:1000D000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D990
:1000E000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D980
:1000F000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D970
:10010000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E68F
:10011000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E67F
:10012000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E66F
:10013000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E65F
:10014000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E64F
:10015000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E63F
:10016000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E62F
:10017000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E61F
:1001800039393939393939393939393939393939DF
:1001900039393939393939393939393939393939CF
:1001A00039393939393939393939393939393939BF
:1001B00039393939393939393939393939393939AF
:1001C000393939393939393939393939393939399F
:1001D000393939393939393939393939393939398F
:1001E000393939393939393939393939393939397F
:1001F000393939393939393939393939393939396F
:1002000013131313131313131313131313131313BE
:1002100013131313131313131313131313131313AE
:10022000131313131313131313131313131313139E
:10023000131313131313131313131313131313138E
:10024000131313131313131313131313131313137E
:10025000131313131313131313131313131313136E
:10026000131313131313131313131313131313135E
:10027000131313131313131313131313131313134E
:100280001E1E1E1E1E1E1E1E1E1E1E1E1E1E1E1E8E
..... till the end


>
> 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)).
>

I mapped the pins on the board so as to be reasonably certain
that the ROM chip was compatible with the 27cXXX series of chips

all the pin/address/data lines seem to be consistent with the
27cXXX series pin out. the data and address lines match to the
MCU adressing pins according to 27cXXX datasheet even the funny 8
through 11 pin jumble.

(pin 22) ROM goes to (pin 29) 8051 (PSEN- prog store enable)
(pin 20) ROM goes to (pin 30)8051 (ALE-Addr Latch Enable)

on the PCB the 8 data lines are all connected with the first 8
Address lines
so D0 is connected to A0 and (D1 to A1) and these shared
connection s all go back to MCU


> 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...
>

thanks for the help,
robb

"mpm" <mpmillard@aol.com> wrote in message
news:08ba70e9-b057-4d39-9962-7f2aafba453f@e25g2000prg.googlegroups.com...
On Dec 27, 2:28?pm, "robb" <s...@where.on.net> wrote:

> thanks for any help i ?am stuck again,
> 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

Utter rubbish.....the 8031 isn't reading sig bytes...
Your programmer is not reading the eprom correctly.

robb wrote:

> <gqrxzy8974@ftml.net> wrote in message
> news:e16006dc-aebf-4d57-8a46-8a1e9409e066@e23g2000prf.googlegroups.com...
>
>>>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)
>>
>>That doesn't sound odd as pin 1 would be A15 on the next
>>size up ROM.
>>
>
> i think i may not be clear ?
> i am saying pin 1 and pin 27 of the memory chip are connected on
> the controller board so that would cause special consideration if
> one wanted to use a 27c512 ?
>
>
>>>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 ??
>>
>>OK, so that's not the problem.
>>
>>
>>>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.
>>
>>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.
>>
>
>
> close , it is a series of sections of 64 duplicate bytes
> followed by another section of 64 duplicate bytes..... all the
> waty to the end
>
> each section of byte values is different and i get the exact
> same series for each successive chip reading attempts.
>
> unless i choose a different chip size like 27c128 then the series
> of byte duplicates changes. where the first set maybe 7A in place
> of the 02
>
> here is a clip from begining of my read
>
> :020000040000FA
> :1000000002020202020202020202020202020202D0
> :1000100002020202020202020202020202020202C0
> :1000200002020202020202020202020202020202B0
> :1000300002020202020202020202020202020202A0
> :100040000202020202020202020202020202020290
> :100050000202020202020202020202020202020280
> :100060000202020202020202020202020202020270
> :100070000202020202020202020202020202020260
> :10008000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9E0
> :10009000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D0
> :1000A000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9C0
> :1000B000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9B0
> :1000C000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9A0
> :1000D000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D990
> :1000E000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D980
> :1000F000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D970
> :10010000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E68F
> :10011000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E67F
> :10012000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E66F
> :10013000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E65F
> :10014000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E64F
> :10015000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E63F
> :10016000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E62F
> :10017000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E61F
> :1001800039393939393939393939393939393939DF
> :1001900039393939393939393939393939393939CF
> :1001A00039393939393939393939393939393939BF
> :1001B00039393939393939393939393939393939AF
> :1001C000393939393939393939393939393939399F
> :1001D000393939393939393939393939393939398F
> :1001E000393939393939393939393939393939397F
> :1001F000393939393939393939393939393939396F
> :1002000013131313131313131313131313131313BE
> :1002100013131313131313131313131313131313AE
> :10022000131313131313131313131313131313139E
> :10023000131313131313131313131313131313138E
> :10024000131313131313131313131313131313137E
> :10025000131313131313131313131313131313136E
> :10026000131313131313131313131313131313135E
> :10027000131313131313131313131313131313134E
> :100280001E1E1E1E1E1E1E1E1E1E1E1E1E1E1E1E8E
> .... till the end
>
>
>
>>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)).
>>
>
>
> I mapped the pins on the board so as to be reasonably certain
> that the ROM chip was compatible with the 27cXXX series of chips
>
> all the pin/address/data lines seem to be consistent with the
> 27cXXX series pin out. the data and address lines match to the
> MCU adressing pins according to 27cXXX datasheet even the funny 8
> through 11 pin jumble.
>
> (pin 22) ROM goes to (pin 29) 8051 (PSEN- prog store enable)
> (pin 20) ROM goes to (pin 30)8051 (ALE-Addr Latch Enable)
>
> on the PCB the 8 data lines are all connected with the first 8
> Address lines
> so D0 is connected to A0 and (D1 to A1) and these shared
> connection s all go back to MCU
>
>
>
>>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...
>>
>
>
> thanks for the help,
> robb
>
>

It would seem your original rom has an internal address latch.
There is *some* evidence that 23256 roms with this feature may have been
used by HP, but I have had no success finding a NEC data sheet for your
rom. This would explain why the eprom reader reads the same value 64
times and also why there is no 8 bit latch chip between the multiplexed
d0-7/A0-7 MCU bus and the rom's A0-7 address inputs. Try a different
algorithm for reading the rom on the programmer. When you've go the
correct contents that dissasemble to something reasonable, you'll need
to put a little board together to insert a latch between the combined
bus and the adddress pins, then program a 27c256 and try it.

HTH

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:
'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed,
All varnished hot moulded wooden racing dinghy.

robb wrote:

> here is a clip from begining of my read
>
> :020000040000FA
> :1000000002020202020202020202020202020202D0
> :1000100002020202020202020202020202020202C0
> :1000200002020202020202020202020202020202B0
> :1000300002020202020202020202020202020202A0
> :100040000202020202020202020202020202020290
> :100050000202020202020202020202020202020280
> :100060000202020202020202020202020202020270
> :100070000202020202020202020202020202020260
> :10008000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9E0
> :10009000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D0
> :1000A000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9C0
> :1000B000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9B0
> :1000C000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9A0
> :1000D000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D990
> :1000E000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D980
> :1000F000D9D9D9D9D9D9D9D9D9D9D9D9D9D9D9D970
> :10010000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E68F
> :10011000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E67F
> :10012000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E66F
> :10013000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E65F
> :10014000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E64F
> :10015000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E63F
> :10016000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E62F
> :10017000E6E6E6E6E6E6E6E6E6E6E6E6E6E6E6E61F
> :1001800039393939393939393939393939393939DF
> :1001900039393939393939393939393939393939CF
> :1001A00039393939393939393939393939393939BF
> :1001B00039393939393939393939393939393939AF
> :1001C000393939393939393939393939393939399F
> :1001D000393939393939393939393939393939398F
> :1001E000393939393939393939393939393939397F
> :1001F000393939393939393939393939393939396F
> :1002000013131313131313131313131313131313BE
> :1002100013131313131313131313131313131313AE
> :10022000131313131313131313131313131313139E
> :10023000131313131313131313131313131313138E
> :10024000131313131313131313131313131313137E
> :10025000131313131313131313131313131313136E
> :10026000131313131313131313131313131313135E
> :10027000131313131313131313131313131313134E
> :100280001E1E1E1E1E1E1E1E1E1E1E1E1E1E1E1E8E
> .... till the end

Looks like gibberish to me.

What happens if you try reading it as a 27C512 ? Just an idea.

Graham