Prom dates, er codes

rauscher at icst.com rauscher at icst.com
Fri Jan 22 13:51:20 GMT 1999



Bruce wrote:
>As I understand proms, a 27C128, and 27128A are functionally
>the same, meaning they share CMOS technology.
>  Anything else may have a different programming voltage, and
>maybe of a slower operating speed??..
>
>  On the few 512 proms I've seen they have all been "27512s", with
>no As or Cs?.   The ""s are cause I not absolutely sure of that.
>Thanks     Again reference to gm type memcals
>Bruce

OK, EPROM's and the codes, it can be a mess. For the following information I'm
using the National Semiconductor Memory Databook as a reference (1988 version).

Without the 'C' in the middle, IE: 27C256, it is NOT a CMOS EPROM. It is most
likely a NMOS part. 

As far as suffix's go:

    'B' is used for a higher speed version of an EPROM, for programming (500usec
prog pulse)
    'C' is for a very high speed version (access and prog pulse[100usec])
    'N' is used for a one time programmable
    'Q' is the package/window type, quartz
    'E' is for extended temp range
    'M' is for a military part, even greater temp range

(Can't find what National uses the 'A' for, although they do use it, their '512
is only
available as an 'A').

These suffix's can be combined:

    27C64BQM    high speed prog, quartz window, military temp range
    27C256QE    quartz window, extended temp range

National EPROMs also use NMC for a prefix: "National, Memory, Cmos"

After the letter suffix's, you will find some digits that define the access
speed of that part. This will be either 2 or 3 digits. This is the access
speed in nano-seconds.

Some full numbers:

    NMC27C512AQ120:

        120 nsec access time
        VCC = 5V +- 10%, 0C - 70C op range (commercial)
    

    NMC27C256CQ55

        55 nsec access time
        VCC = 5V +- 10%, 0C - 70C op range 


You can find additional information at Atmel's and Nationals' web sites. The
different
programming algorithm's can be interesting reading.

When I obtained EPROMS for this EFI project, I specified all National EPROMs
so that I could setup the programming for one chip manufacture. (I built my own
programmer). They are mostly the standard 27C256's with some 'E's mixed in.


HTH

BobR.

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