Can anybody suggest what the part number of such a device could possibly be?  - Page 1
Forum section: electronics / projects

author: pbarton
author_rank: Frequent Contributor
timestamp: March 01, 2023, 04:44:33 pm
content: 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?

author: coromonadalix
author_rank: Super Contributor
timestamp: March 01, 2023, 05:34:51 pm
content: https://www.digchip.com/datasheets/parts/datasheet/222/QS34XST253.phpQS34XST253?is it a keyboard matrix switch ?

author: pbarton
author_rank: Frequent Contributor
timestamp: March 01, 2023, 05:49:50 pm
content: 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?

author: pbarton
author_rank: Frequent Contributor
timestamp: March 03, 2023, 07:29:48 pm
content: Some multiplexer chips here:https://en.wikichip.org/wiki/multiplexer#Large_MultiplexersBut no 32 to 8 based mux on a single 48 pin chip. Still looking.

author: MarkS
author_rank: Unknown
timestamp: March 03, 2023, 08:41:00 pm
content: It may have been a CPLD.

author: pbarton
author_rank: Frequent Contributor
timestamp: March 04, 2023, 03:23:32 pm
content: According to this articlehttps://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.

author: JDubU
author_rank: Frequent Contributor
timestamp: March 04, 2023, 03:57:36 pm
content: Could it be an octal 4:1 multiplexer?

author: Haenk
author_rank: Super Contributor
timestamp: March 04, 2023, 05:00:26 pm
content: 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?

author: pbarton
author_rank: Frequent Contributor
timestamp: March 04, 2023, 07:32:58 pm
content: 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 .pdfhttp://wwww.bitsavers.org/pdf/dec/pdp15/hardware/VT15_EngrDrws_Oct77.pdfThe drawing is identified as CHARACTER GEN READ ONLY MEMORY. VT15-0-41Unfortunately the Chip ID and the chip pinout is not identified.There is also a VT15 Maintenance Manual which mentions the 32:8 muxhttp://www.bitsavers.org/pdf/dec/pdp15/hardware/EK-0VT15-MN_VT15maint_Jan74.pdfpage 5-9 Para 5.1.S Thirty-Two to Eight Bit Multiplexer M761Sorry 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.

author: MarkS
author_rank: Unknown
timestamp: March 04, 2023, 08:50:44 pm
content: 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.

author: Haenk
author_rank: Super Contributor
timestamp: March 05, 2023, 12:21:36 pm
content: 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 checkhttp://www.compsy.de/moduls/dmodul1a.htmfor similar "M" cards; unfortunately this M761 is missing; maybe derive from a M734?

author: pbarton
author_rank: Frequent Contributor
timestamp: March 05, 2023, 03:24:03 pm
content: 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.