RE: [N8VEM-S100:3711] ALTAIR/IMSAI 8080 CPU replacement board

Hi Guys,

Well I'm finally done laying out this board. The autorouter only produced swiss cheese with over 900 via's. It looked terrible!
Anyway, I scrapped everything the autorouter did initially, and proceeded to layout the traces manually. Once I got what I thought was all the hard parts done, I let the autorouter have another go at it. Again it did not work out so well and it was unable to complete the board, so I proceeded to undo it's changes and/or improve it's routing manually. I squeezed those traces in there tight, any tighter and they'll be popping off the board. Anyway, I'm working on the silkscreen layer and ready to do a run.
Here's a picture of the board layout....
You can see the serial port connections on the top left, SD card to the right of the 27C256 EPROM, parallel ports next to that and the ALTAIR and IMSAI front panel connectors. There are also a few jumpers around the board to configure for CPU or Peripheral board only and ALTAIR/IMSAI mode. Firmware for the board will be my next project, but I have to make preparations for VCF-MW my priority. Dave Ruske and I will be doing a COSMAC 1802 exhibit there in September.

Cheers,
Josh Bensadon

From: crus...@hotmail.com
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:3711] ALTAIR/IMSAI 8080 CPU replacement board
Date: Sun, 18 May 2014 00:57:20 +0000

Hi Guys,

Well, this project has just reached a milestone. The hardware is tested and working. I had some rewiring to do to make it work for the ALTAIR, I thought the ALTAIR and IMSAI front panels were (near) identical, but they are not.
There are some jumpers on the board to configure between ALTAIR and IMSAI.

Here's a picture of my debugging and testing setup. The board is being tested in the ALTAIR.

Now entering Phase 2... building a PCB.

Cheers,
Josh Bensadon

From: mon...@vitasoft.org
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:3666] ALTAIR/IMSAI 8080 CPU replacement board
Date: Tue, 13 May 2014 13:56:05 -0700

Very nice Josh!

John

From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Tuesday, May 13, 2014 1:19 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:3664] ALTAIR/IMSAI 8080 CPU replacement board

Hi Group,

Well, I'm cooking up this board at the moment. I have all the hardware figured out to run like the original CPU boards.
I need to do a little more testing of the hardware, then I'll proceed to building the boards.
The Memory, I/O, UARTs and SPI interface to the SD card appear to all be working.
8K chunks of memory can become either ROM, RAM or mapped off the board.

CPU: 8080A
UARTS: 2x 8250
RAM: 2x 32K
ROM: 32K
I/O: 8 input, 6 output pins
SPI to SD Card interface
ALTAIR & IMSAI Front Panel Connectors.

Where ROM is selected in a block it overlaps the RAM on reads, but writes go through to RAM.
The ROM can then be disabled and reads will come from the RAM at that location.
The firmware is copying itself to RAM then switching off the ROM.
The CPU can be deselected with jumpers and the board will work as RAM/ROM and I/O for another CPU on the bus.

Pictures attached. Yellow-Data, Brown-Address, Blue-I/O, Green-Control/Status & everything else.

Regards,
Josh Bensadon

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