18 Nov
2010
18 Nov
'10
9:06 p.m.
Well, since Tony did not mention it ... I did this
long ago, and I remember
Im general I like to keep things as original as possible. So while I'd
replace a 4116 with a 4164 if I couldn't get the former, I wouldn't
replace a set of them for no good reason.
Not beinvbe able to provide the +12V and -5V would be a 'good reason'.
But the OP's PSU supplies thece voltages..
FWIW, there were 5V-only 16K*1 DRAMs. (4816 IRIC).
that Tony has told about this here too, not so long
ago :-/
Since the 4116 are in sockets, remove them! If you replace them with 4164
you can get rid of the -5V power supply, and IIRC also the +12V power
supply.
Yes, the 414 uses +5V only.
There are a few pins (2 or 3) of all 4116 sockets that
must be tied together
or to some level (GND or +5V).
Basically, you disconnect the -5V supply from pin 1 (and leave pin 1
floating, it doesn't matter if the pin 1's on all the DRAMs are linked
together thougn) and disconnect pin 8 from the +12V supply and reconnect
it to +5V. Pin 9 is the other pin that differs between the 2 types ofRAM,
it's +5V on the 4116 and A7 on the 4164. If you'r only using 1/4 of the
IC, you can leave that as-is, if you want to make use fo all the 64K
chip, you have to feed another multiplexed address line in there.
If you do that, you must remove all the decoupling capacitors on that
line, otherwise the timing will be all over the place. This led me a
merry dance on an Epson QX10 video board some time back...
Oh yes, 4116s (not suprisingly) use 7 bit refresh. 4164s use either 7 bit
refresh or 8 bit refresh. If the latter, you can still use 1/4 of the IC
and just keep the 7 bit refresh (this will refresh half of the IC,
including the 1/4 you are actually useing). But if you want to use the
whole chip, you may have to modify the refresh circuit too.
4164 are not expensive and it solves the triple
voltage issue very nice.
If you have the schematics you could even add a few switches or output lines
and have a form of "bank switching".
Or just accept that 3/4 of the available RAM is not used :-)
But as I said above, I'd not do this. Keep thigns as origianl as
possible. Otherwise you might as well replace all classic computers with
emulators and not keep the old hardware running at all...
-tony