MP-LA Parallel Interface

The MP-LA Parallel Interface is a 5 1/4 inch x 3 1/2 inch board implemented with the 6820 peripheral interface adapter integrated circuit which is used to interface a parallel data device to the computer. The board is provided with two separate connections along the edge of the board. Each connector contains eight data lines which may be programmed for either outputs or inputs, one "data ready" line, and one "data accepted" line for full handshake control. All data lines are fully buffered with bi-directional transceivers to allow eight inputs and eight outputs, 16 inputs and no outputs or 16 outputs and no inputs. Programming of a particular set of data lines is done via jumpers on the MP-L board. Software control of interrupt lines and the polarity of the handshake lines is provided.

The original M6800 family of ICs used enhancement-mode MOSFET technology that was limited to 1MHz. In early 1975 work began on a redesign using depletion-mode technology. This reduced the die size and allowed operation at 2MHz. Internally the project was known as MC6800D but the fasters parts were release in 1976 as the MC68A00 (1.5MHz) and MC68B00 (2.0 MHz). The all of new parts were backwards compatible except a slight change in the I/O pins of the PIA chip. The MC6820 became the MC6821 because the electrical characteristic of PA0�7 and PB0�7 pins changed slightly. The typical Input High Current went from -250 μAdc to -400 μAdc and the Input Low Current went from 1.0 mAdc to 1.3 mAdc.

Introduced by Southwest Technical Products Corporation in 1976. The MP-LA kit cost $35

Board Photo (49k JPG)

Board Photo High Resolution (160k JPG)

Assembly Instructions (113k PDF)

Schematic (200k PDF)

Advanced Information: 1.5 and 2.0 MHz Components for the M6800 Microcomputer System  (521k PDF)

Announcement of the MC6800D in the March 4, 1976 issue of Electronics magazine (290k JPG)

SWTPC 6800 Components
Michael Holley's SWTPC Collection Home Page
This page was last edited August 14, 2013