I'm working a 4-bit GPU, the GPU run on 1.023MHz (1023kHz) clock while CPU only run on 127kHz so I need a screen buffer for it when the CPU is working on some instruction. The display I use is a 24 x 16 pixels display so I need at least 4 x 24 x 16 bits or 1536 bits cause it's have 4 bits color. I'd like the 74ls189, this chip have separate input, output and a parallel address line so I don't need a switching circuit which reduce the controll line for the CPU, but the thing is that the 189 is only 16 x 4 bits so I would need like 24 of them for the screen. I found a few option but most of the are 8 bits ram and input-output on the same line So I want to ask if anyone know a chip that similar to the 74ls189 (a 4 bits static random access memory (SRAM); have separate input, output and a parallel address line; a chip select, input enable, output enable; able to working at 1.023MHz or higher) but have like 512 x 4 bits or 2048 bits. I'm fine with a chip like 256 x 4 or 128 x 4 bits. If could, I also want the chip is in the production stage and have a open datasheet cause there's not much information about the 74ls189 and I think that chip is obsolete.

  • \$\begingroup\$ Sorry, recommendations for specific products are off-topic for this site. \$\endgroup\$ Dec 16, 2021 at 14:13
  • \$\begingroup\$ You've made a list of the parameters you care about. Were you able to search them in a parametric search on a site like digikey or mouser, and if so, what problem did you encounter? Did you have too many results? Too few? Unsure how to map your parameters to the parameters in the search? Unsure how to interpret the results? \$\endgroup\$
    – nanofarad
    Dec 16, 2021 at 15:14
  • \$\begingroup\$ @nanofarad like I mention, most of the answer are 8 bits chip while I'm researching for 4 bits chip. I did find a few that pretty promising but they are hard to find or obsolete. I've already ask in a few other forum but I haven't seen any good answer for what I'm looking for \$\endgroup\$ Dec 16, 2021 at 15:19
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    \$\begingroup\$ Why can't you use an 8-bit chip and just ignore four of the bits? \$\endgroup\$
    – Hearth
    Dec 16, 2021 at 16:12
  • \$\begingroup\$ @Hearth, The 8 bits is fine but most of themhave the input-output on the same line, I want the chip that have separate input-output. I do fine some chip that good but they quite complicate to control and because I want to reduce control line of the machine for the GPU since it's only have 8 line to it and I don't want to use switching circuit \$\endgroup\$ Dec 16, 2021 at 16:34

1 Answer 1


What you need to search for is a "dual port" RAM.

You can get 32K x 8 bit dual port RAMs on major distributors like Digikey and Mouser for under $1. They will all be SMD though.

  • \$\begingroup\$ Thanks but I might use other option since my machine is a prototype and so smd components is not a good option cause I need to troubleshoot a lot. \$\endgroup\$ Dec 16, 2021 at 16:44
  • \$\begingroup\$ @SairextIrkaris You might be able to buy an SMD to through hole adapter. For example, the 7134SA55JG 4K x 8 dual port SRAM or CY7C141-55JCT 1K x 8 dual port SRAM both come in a PLCC-52 package, and you can get a PLCC-52 through hole socket for like $2. \$\endgroup\$
    – user4574
    Dec 17, 2021 at 3:30

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