TMS4500A DRAM Controller Datasheet needed
ard at p850ug1.demon.co.uk
Sun Jul 26 13:26:16 CDT 2009
> I'm looking at a memory expansion board for a PCjr that uses this chip
> and I have found a pinout of it from the data sheet archives, but I'm
> having some confusion that a real data sheet or application note would
> clear up. (Specifically the sheet that I found says it supposed up to
> 64Kbit DRAMs, but this board is constructed with 256Kbit DRAMS.)
> Does anybody have an version of the full data sheet and application
> notes that they can send me a copy of?
I have the data sheet on paper (in a TI memory databook), but I notice
that Al has put it on-line, so I don't need to copy it.
I've worked on the memory expansion PCB for the HP Integral, which uses
this DRAM controller along with 256Kbit DRAMs, and I can describe what
was done there...
The basic problem is the the TMS4500 only has an 8 stage address
multiplexer, providing 8 address outputs to the DRAMs. This is fine for
64K bit chips, but of courseyou need 9 bits for a 256K bit DRAM. So you
add an external address multipexer chip (a '157 or '158), the problem is
finding the signal to swtich it, since that signal is not brought out of
What HP did was to switch the multiplexer using the CAS output of the
TMS4500. One section of the mux provided another address line to the
DRAMs, a second section had one input tied high and the other tied low.
The output of that followed the select input (and thus the CAS output of
the 4500), but with a slight delay (due to the propagation delay of the
multiplexer). This was delayed slightly more and used to vide the CAS
signal to the DRAMs (the extra delay ensured all address lines had
settled before CAS was asserted).
I hope that gives you some hints as to what to look for...
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