Can anybody suggest what the part number of such a device could possibly be?

[pbarton]

Looking for the ID of a multiplexor chip that must have been available around 1970.
32 inputs-to-8 outputs. TTL, probably DIP package. 48 pin chip.
Can anybody suggest what the part number of such a device, could possibly be?

[coromonadalix]

https://www.digchip.com/datasheets/parts/datasheet/222/QS34XST253.php

QS34XST253

?
 is it a keyboard  matrix switch ?

[pbarton]

No, not a keyboard matrix switch.
QS34XST253 appears to be 80 pin and the one I'm looking for is definitely 48 pin.
It was used in a vector graphics controller.
I guess that it's been obsolete for the last 20, 30 or 40 years?

[pbarton]

Some multiplexer chips here: https://en.wikichip.org/wiki/multiplexer#Large_Multiplexers
But no 32 to 8 based mux on a single 48 pin chip. Still looking.

[MarkS]

It may have been a CPLD. 

[pbarton]

According to this article https://www.eejournal.com/article/how-the-fpga-came-to-be-part-2/
CPLD’s, FPGA’s and MPLA’ s were invented around 1973 or 1975.
The device I’m looking for was available in 1970. Many thanks for your help.

[JDubU]

Could it be an octal 4:1 multiplexer?

[Haenk]

Honestly , these breadcrumbs are not a great start.
Which year are we talking about? 1970? Or maybe 1975 or even 1979? That would make a *huge* difference in manufacturers to check for.
Which "vector graphics controller" are we talking about? Make, model, year, target system? Maybe even a picture?

[pbarton]

The Digital Equipment PDP15 was announced in 1970. The VT15 display controller contains a M761 module, on which the 32:8 mux resides.
There is a schematic about half way down this .pdf   http://wwww.bitsavers.org/pdf/dec/pdp15/hardware/VT15_EngrDrws_Oct77.pdf The drawing is identified as CHARACTER GEN READ ONLY MEMORY. VT15-0-41
Unfortunately the Chip ID and the chip pinout is not identified.
There is also a VT15 Maintenance Manual which mentions the 32:8 mux  http://www.bitsavers.org/pdf/dec/pdp15/hardware/EK-0VT15-MN_VT15maint_Jan74.pdf page 5-9  Para 5.1.S Thirty-Two to Eight Bit Multiplexer M761
Sorry no photo of the M761 module. If I knew of any surviving PDP15 I could have asked the owner to unplug the module and identify the chip.

[MarkS]

I'm willing to bet it was a custom chip. Your best bet will probably be 4 8:2 muxes. If the footprint is critical, make a small PCB with SMD components and headers.

[Haenk]

I'm willing to bet the M761 is "yet another" FlipChip module, so you are not looking for a single IC, but a TTL logic based whole PCB.

You might want to check http://www.compsy.de/moduls/dmodul1a.htm for similar "M" cards; unfortunately this M761 is missing; maybe derive from a M734?

[pbarton]

Digital was more than capable of implementing a 32:8 bit mux on "yet another" FlipChip module, using several TTL components. Along the lines of the M734.
However, from a previous life, I know that the M761 contained only one 48 pin chip.
This must have been a custom chip, of some description.
Unfortunately, the M761 is not documented as well as some of the other modules.
Anybody know of a PDP15 with the VT15 display controller, in private hands or within a museum?
Many thanks for all the constructive comments.