Help me identify an IC without the part number

[MCMC]

Unknow IC

Hi

I have electronic circuit uses Z80 cpu that one ic the part number is erased whit sandpaper, but below have the name engraved (Portugal) is a 20 pin it's connected at the output data (D0, D7) of 27c256 Eprom and the output of this go to some ic's like 74ls374,
anybody helpme

 

[Dspnut]

I am not sure, but, my guess is that this IC may be a programmable logic device like a PAL or GAL. :? ???

 

[jzaghal]

Hi,

I would guess it is a 74LS373. But without the circuit in front of me
it is difficult to say !!

GoodLuck.

 

[MCMC]

Hi all Thanks for reply
here the circuit

 

[thomaz]

looks like a kind of copy protection....
scramble the contents of EPROM and descramble it with this magical device
you can copy the PCB and copy the EPROM, but without this IC ... :-(
very nice idea to protect your work from being stolen
it must be a GAL !?
to get around it:
put it in a breadboard, apply all 256 possible combinations of input data and record the output
then strain every nerve and find the boolean equations
that's the way...

or am I wrong?

 

[johnyaya]

My past experience with altered device labels is that they are altered because you can purchase them and then copy the circuit yourself. Sometimes (if you're lucky) you can pick-up on the part number or at least a partial if you use hi-power magnification.

 

[petarpav]

May be TTL prom like 82S....

 

[sc/mp]

I've seen many TTL from Texas Instrument made in Portugal
Regards

 

[MCMC]

Hi all and thanks

another possible test is disconect the ic and jump all the data lines ?

mcmc

 

[thomaz]

hahahahahaha......

if it works, I will return my graduation to university ;-)

(not really)

 

[sc/mp]

If it works.... you could also remove Z80 and EPROM and
put all the pins to ground (except Vcc off course !)........

More serious : if you disconnect your chip put it on a
breadboard and try to find inputs / ouputs then compare
with possible candidats. Apply levels/edges on inputs.

May be somebody near you has an old Eprom programmer
with TTL chip identification / test function. I presume your
chip is a TI TTL.

Regards

 

[MCMC]

Hi all and thanks

this circuit is manufactured aproximately in 1985, because the sistem show the date when is powerup, and go to test all output leds display etc!!

another posible method to check it is to know what companys stay in portugal for this period