Unknown ICs - SP8918 and SP8924

[Singapura]

Hi everyone

I am working on an old NCR ISA bus SCSI host adapter board and there are these two ICs with old National Semiconductor logo, with part numbers and date of manufacture as follows:

SP8918 W0371
SP8924 W0691

I have searched archived sites for scanned old NS data books but so far no luck. Wonder if anyone know or have datasheets on this two ICs?

Thanks!

 

[betwixt]

Those are probably house codes rather than generic part numbers. I would guess the 'SP' numbers are the year 89 and week number of production and the 'W' is the part identification.

Can you post a photograph of the card and point out the two IC's, it might be possible (no promises) to work out what their function is and suggest possible alternatives.

Brian.

 

[Singapura]

Hi Brian

Thanks for replying. Here is a photo of the board with the two ICs enlarged:



You can see the National Semiconductor logo on both ICs.

Hope to hear some good news!

 

[betwixt]

I'm afraid I drew a blank.

I can identify and guess the purpose of most of the parts except the bus address decoding and that might mean the ICs are PALs or PROMs used to select the card address. If that is the case, even if you had a generic part number it would be for a blank device and you would still need the program to put inside it. Given it's age, it would almost certainly be a fusible link PROM and even finding a machine to program them is difficult these days.

Brian.

 

[Singapura]

Hi Brian

You may be right about that.
I've attached part of the schematic which I reverse-engineered just to get a better idea.



Thanks for your help! Much appreciated.

 

[betwixt]

They appear to be steering and maybe latching the DMA signals so they are only activated at certain addresses so the PROM hypothesis looks likely. Curiously, it seems that if the wrong combination of switches are turned on it can crash the system by linking the request and acknowledge lines together!

I think you might be out of luck if this is a repair job.

Brian.