Sorry John, misprint should be ~40. Actually at the speed of the ARM you could multiplex the S100 bus signals but 46 would be more than enough to control all S100 I/O boards, DMA lines etc.
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Paul Birkel
John: How does one get from 46 GPIO pins to "~140 lines available"? My (very!) limited understanding is that the non-GPIO pins are firmly committed to specific functions by the ARM processor & support circuitry and, unlike a FPGA, they can not be repurposed. Those GIPO are the (only) lines that the base-board uses to host "wings-n-such" with its dual 0.1" headers.
Mounting the DDR2 SODIMM connector directly on the S-100 board still looks like a SMT challange (0.6 mm pitch), but at least its just one SMT to solder down and thus avoid the dual-connector alignment problem :->.
I *think* that this is the right-angle style that we'd want, placing the SODIMM module parallel to the S-100 board. But I think that one would need a reflow oven to attach it as it seems that the SMT pins are not iron-accessible (note "solder peg" in inset drawing -- which suggests to me that we're talking about the equivalent to a BGA)?
If one can live within the bounds of 46 GPIO, then the S-100 board becomes the single "wing" attached to the pair of 0.1" headers on the "Compute Module IO Board" ... (and the SODIMM Compute Module just nests onto that). For our purposes the SODIMM connector looks like no advantage whatsoever?
I believe that the BBB mentioned earlier has 65 GPIO already available on 0.1" headers? (See: http://www.adafruit.com/datasheets/BBB_SRM.pdf)
How many GPIO are _absolutely_ needed to handle the S-100 bus?
On Thu, Aug 28, 2014 at 10:37 PM, monahanz <mon...@vitasoft.org> wrote:
Well I spent almost 2 days looking at almost every COM (computer on a module) on the web. There are at least 100, probably more. The outfit called "Olimex" seemed to me to have the best systems, their "base board" with on dual 0.1" centers probably could be done on an S100 bus board, The interface did look complicate to me however. Another group "Toradex" also looked good and use what seems to be becoming common COM connector, a SODIMM connector. They have way more types of inputs than one would normally need, again complicating the potential S100 board connection.
Then I discovered that the famous Raspberry Pi is coming out with a SODIMM equivalent of their original custom board. They supply an adaptor board to connect to it for a keyboard, LCD etc. as well. What's really nice is they bring out all the ARM lines to the edge connector, Best of all they released detail schematics of both the CPU board and "base board". The latter I would put on an S100 bus card, and with the ~140 lines available, more than enough to control the S100 bus. I wish they had more RAM on board (512K), but the demo operating system seems fast. See here for more info.
Another nice thing about this setup is there is an enormous hobbiest support group. My fear with some of the other companies is they would never help/give support etc.
Anyway that is my thinking currently for putting an ARM on the S100bus. Comments please!