16 Nov
1998
16 Nov
'98
9 a.m.
On Nov 16, 5:39, Doug Spence wrote:
They're NOT the same. I can't find a pinout, but they're a different
(physical) size and ISTR they use different voltages as well. MPS6550s
will be very hard to find as they were never second-sourced by anyone, as
far as I know. They're 22-pin (0.4" wide instead of 0.3") 4096-bit (1024
x
4) SRAMs. 2114's are 18-pin 4096-bit (1024 x 4) SRAMs.
Even MOS Technology didn't make them for very long, which is why only the
earliest PETs used them.
According to the GIICM (http://www.falstaff.demon.co.uk/giicm.html)
2114 - 1kx4 SRAM.
+---+--+---+
A6 |1 +--+ 18| VCC
A5 |2 17| A7
A4 |3 16| A8
A3 |4 15| A9
A0 |5 2114 14| D1
A1 |6 13| D2
A2 |7 12| D3
/CE |8 11| D4
GND |9 10| /WE
+----------+
And adapted from the PET schematics at
http://www.funet.fi/pub/cbm/schematics/computers/pet/2001/320008-2.gif
+---+--+---+
A0 |1 +--+ 22| VSS (GND)
A1 |2 21| CS1
A2 |3 20| CS2
A3 |4 19| /CS3
A4 |5 6550 18| /CS4
A5 |6 17| VDD (+5v)
Ph2 |7 16| D3
A6 |8 15| D2
A7 |9 14| D1
A8 |10 13| D0
A9 |11 12| R/W
+----------+
While the RCA 1822 looked like this...
(Courtesy of http://www.semi.harris.com/data/pk/pk0/pk0069/)
+---+--+---+
A3 |1 +--+ 22| VDD (+5v)
A2 |2 21| A4
A1 |3 20| R/W
A0 |4 19| /CS1
A5 |5 1822 18| OD
A6 |6 17| CS2
A7 |7 16| DO4
VSS |8 15| DI4
DI1 |9 14| DO3
DO1 |10 13| DI3
DI2 |11 12| DO2
+----------+
I include the 1822 for two reasons - it was used in the original Elf (keeping
this reply on topic ;-) and it has the same package size as the 6550, wide
format 22-pin DIP, vs. standard (0.3") 18-pin DIP for the 2114.
I've been lucky enough to find some old printers and such with older RAMs
in them (No... they weren't working). I have no ready sources for bulk
buys of old RAM.
-ethan
