![S100 Computers](../../../Header/S100_Banner.jpg)
SD SYSTEMS
- ExpandoRAM Dynamic
Memory Cards.
SD Systems
really built the business with their dynamic RAM cards which they called
ExpandoRAM cards. The initial boards utilized 16K dynamic memory chips
(4108's) and could be configured to work with 1,2 3 or 4 banks. This was quickly
increased to 64K RAM chips (4116's). Thereby allowing one S-100 board to take care
of the complete 64K address space of the 8 bit Z80 CPU's used at the time. The boards
were quite configurable and would fit in well with other memory cards within the
64K memory space. They responded to the PHANTOM S-100 line so ROM's on CPU
cards worked fine.
![SD Systems ExpandoRAM](ExpandoRAM-a.jpg)
The boards were sold initially as kits but later were also
sold fully assembled and tested. There were three major version of the board called
the ExpandoRAM, ExpandoRAM II and ExpandoRAM III. Each had numerous revisions.
The ExpandoRAM III was IEEE-696 compatible. Memory access was about 367ns - fast
at that time. The ExpandoRAM-III which came out in 1983 could be configured with
4164 chips allowing for a RAM card capable of addressing 256K of memory. It also
ran with a 4MHZ Z80 with no wait states.
A typical schematic of these boards is shown
here.
The manuals can be seen by clicking on the appropriate pdf
file below.
SD Systems ExpandoRAM-I
manual
SD Systems ExpandoRAM-II
manual
SD Systems
ExpandoRAM-II Update manual
SD Systems ExpandoRAM-III
manual
Howard Adams wrote an article in the Sept 1980 issue of S-100 Microsystems
(Vol 1,#5, p44) describing how to modify the original ExpandoRAM series
(which were designed to run at 2MHZ), to run at 4MHZ. The article can be
obtained here.
Other SD Systems S-100 Boards
8024 VDB
ExpandoRAM
ExpandoROM
SBC
VersaFloppy I & II
Z8800
PROM-100
I/O8 Serial Board
4KRAM
Other Boards
This page was last modified
on 01/08/2011