Outdated SRAM Circuits with Single Byte Width

Discussion in 'General Electronics Chat' started by shalebridge, Jul 6, 2014.

  1. shalebridge

    Thread Starter New Member

    Jul 6, 2014
    4
    0
    Hello all,

    I've been working with very old 1k x 1 SRAM circuits with and without a processor and began wondering how hard it would be to use modern SRAM to modify into the circuit. Not knowing much about memory allocation systems, especially in CPU and controller-less designs, and finding 1 byte width versions hard to come by, I was curious if there was any way to use other byte width designs in single 1k x 1 designs. Extra logic is fine if clocking adjustments are needed, but I think it would be preferable to try and find a way to use new chips instead of finding NOS or pulled 6508/2125/2115A/UPD443 etc...
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,155
    1,795
    Not hard at all. You just ground all the address inputs above the 1K boundry.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    6116 2k x 8 and 6264 8k x 8 SRAM are still readily available.
     
  4. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    I got some 5114 (cmos version of 2114 1Kx4 sram) free from Mr Lee Harts of the Yahoo 1802 COSMOS few years ago. you only need 2 to make 1Kx8. I also have some 2114 left over from my OSI C1P machine.

    Allen
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    I have some sharp 4 bit SRAMs here, SOIC28, and they need 150mA each.

    You can use them just connect pullup's to the other 3 bits, and only use one.
     
  6. shalebridge

    Thread Starter New Member

    Jul 6, 2014
    4
    0
    Thanks for all the quick replies. I had actually thought about using the 6264, and the idea of grounding the other I/O pins had crossed my mind, but here is where I feel it gets tricky...

    The 6508 has separate Data In and Data Out ports and 10 address inputs for 1k x 1. A5-A9 seem to be row addressing, and A0-A4 column decoding.
    [​IMG]

    The 6264 has 8 two-way I/O ports and 13 address inputs for 8k x 8. A4-A9, A11-A12 are row addressing, and A0-A3, A10 column addressing.
    [​IMG]


    I can see using the same I/O port using a DPST analog switch when W is high, but the addressing seems tricky. Both use 5 inputs for column decoding, but the 6508 uses 5 row inputs and the 6264 uses 8. Would this mean that each row of the 6264 would be 1k, and if so, how would the five address inputs in the original circuit work with this?


    I may take you guys up on the memory offers actually, but I want to get the basic idea of how one would shoehorn a new SRAM into an old circuit. Discrete/analog and digital circuits I know really well, but any opportunity to learn more about something like memory interfacing I can't pass up. Plus I like the idea of memory expansion in something like a Oberheim OB-1 or an old arcade machine.
     
    Last edited: Jul 7, 2014
  7. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    I didn't read your post carefully enough. What are you actually attempting to do?
    If you simply need 1k x 1 SRAM chips I might have a bunch to give away.
     
  8. shalebridge

    Thread Starter New Member

    Jul 6, 2014
    4
    0
    What I want to try and do is see if it would be possible to use say, the 6116 2kx8 or 6264 8kx8 for example, in a circuit designed for the 6508 1kx1. I could definitely make use of extra original 1k x 1 chips, but my end goal is to figure a way to use new parts. I know that NTE made a 6508 clone, or at least sells relabeled NOS ones, but the fact that they aren't widely available on sites like Mouser make me wonder about the remaining supply.
     
  9. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    385
    I don't see where you see rows and columns in the addressing of the 6508 and 6264. These look like static memories going by the pin names. All of the address inputs of a static RAM are the same.

    If they were dynamic RAM then rows and columns would make sense. Dynamic RAM's have /RAS and /CAS input pins to latch the row and column addresses inside the RAM from an external multiplexed address bus.

    A curious fact: The address lines of a static RAM are interchangeable. The RAM only cares that the data written to an address is the same when read back from that address. This can be used to advantage when laying out a memory array on a PCB.

    Note that the address lines of a ROM are _not_ interchangeable. A ROM requires that the pre-stored data come from a known address in the memory.
     
  10. shalebridge

    Thread Starter New Member

    Jul 6, 2014
    4
    0
    The block diagram for each chip was where I assumed row/column addressing:

    6264
    [​IMG]

    There is a similar one for the 6508 on the A pins.
     
  11. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    385
    OK, I see where you got the idea about rows and columns. The block diagram implies that the timing of rows and columns might be different. I would not be surprised if the same block diagram is used for many different products from the same manufacturer. You don't want to put too much faith in the absolute accuracy of this drawing.

    In practical circuits what you call each address pin does not matter. If you look at the data sheet you will see that it gives the same delays, set up or hold times for all of the address pins. Because the data sheet makes no distinction between the address pin timings, each manufacturer of an equivalent memory chip is free to choose how the pins connect to the memory cell array.
     
  12. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    you can treat 2k x 8 as 8x 2k x8, and simply disregard (means not use) 7 of them.

    No one forcing you do to something with bits you dont need, except you should pull them up or down.

    your 1k x 1 RAM orignally would be rather slow, not 15 nsec like some 32k byte SRAMs.

    They are kind of obsolete, many controllers nowadays have internal memory that large, and also serial RAMs are used.

    But unless 1bit- wide SRAM they will be available for another 10 years or so.

    Some are still being made, and distributors offer them.

    Is it really that important to use 1bit wide RAM?

    Isnt it in the end used to form 8bit memory? Do you just want to keep the original circuit board?

    If you are going to make new boards, you dont need to use 1bit wide, and if you repair boards which use 1bit wide, I guess there wont be so many at all.
     
Loading...