MP-A Microprocessor / System Board

The SWTPC MP-A board is the primary logic board for the system. It is a 5 1/2 inch x 9 inch circuit board containing the 6800 microprocessor chip, the 6830 ROM which stores the Mini-Operating system and the 6810 128 byte scratch pad memory for the ROM. There is a crystal controlled processor clock driver and baud rate generator providing serial interface baud rates of 110, 150, 300, 600 and 1200 baud. The board also contains a power up/manual reset circuit which loads the ROM stored operating system when activated. Full I/0 buffering is provided for the 16 address lines and 8 bi-directional data lines with those and other interconnections made to the rest of the system thru a fifty pin connector the mother board (MP-B).

Introduced by Southwest Technical Products Corporation in 1975 and cost $200 in kit form.

This original board came with the Motorola MIKBUG ROM (MC6830L7) but many boards were modified to take SWTPC SWTBUG ROM. This was a simple modification and is described in the SWTBUG documentation. The MIKBUG has an * prompt while SWTBUG has an $ prompt.

Another common modification was to disable the 128 byte RAM (MC6810) that was located at hex address A000. This was done for the FLEX 2.0 disk operating system that required 8K bytes of memory starting at A000.

Board Photo (JPG 55K)

Board Photo High Resolution (JPG 415K)

Assembly Instructions (6 pages PDF 15K)

Red Blue Board Layout (JPG 158K)

System Checkout (6 pages PDF 20K )

MIKBUG Engineering Note 100 (23 pages PDF 180K)

MIKBUG Source Code (TXT 9K)

Modifying the MP-A for FLEX (PDF 174K)

Modifying the MP-A for SWTBUG (PDF 155K)

SWTBUG ROM Photo (JPG 21K)

Schematic (JPG 300K)

DS8835 DataSheet (181k PDF)

Michael Holley's SWTPC Collection Home Page