PIA STROBING
Use of the Control Interface for Read/Punch-On/Off Decoding
SWTBUG® software contains subroutines to send out pulses to unused pins of the PIA integrated circuit on the MP-C serial control interface that can be used for automatic reader / punch controls. These pulses can be used if you are using a SWTPC AC-30 cassette interface and a terminal in which access to the control command decoding is denied.
If you intend to use the read/punch control logic output on the MP-C control interface board, make the following connections from the indicated pins of ICI on the MP-C control interface board to the specified pins of a twelve pin male connector shell. The connector pinning shown below is correct for a SWTPC AC-30 cassette interface and will need modifications for other units. Be sure to make the wires long enough to reach your AC-30 where the connector will be plugged. If you have access to your terminal’s 16X baud rate clock, the terminal’s clock bus should be broken and the 16X clock IN and OUT lines brought out to the same connector.
MP-C IC1 pin 7 (read on) | 12 pin male shell female pin 1 |
MP-C IC1 pin 4 (punch on) | 12 pin male shell female pin 2 |
MP-C IC1 pin 6 | (read off) | 12 pin male shell female pin 3 |
MP-C IC1 pin 5 | (punch off) | 12 pin male shell female pin 4 |
Terminal’s 16X clock OUT | 12 pin male shell female pin 5 |
Terminal’s 16X clock IN | 12 pin male shell female pin 6 |
MP-C ground | | 12 pin male shell female pin 12 |
These signals are low going pulses and are about 15 microseconds wide. They are not buffered and should drive a maximum of only one standard TTL load.
PIA stroking will work only on SWTBUG®‘s L, P and E functions. Strobing is not supported in BASIC and some other SWTPC software.
OPERATING THE MP-A2 PROCESSOR BOARD
AT BAUD RATES HIGHER THAN 1200 BAUD
The MP-S Serial Interfaces available for the SWTPC 6800 Computer System are capable of operating at baud rates up to 9600 baud. Although baud rate clocks for 110, 150, 300, 600 and 1200 baud are generated, buffered and fed onto the mother board by IC4 of the MP-A2 board, clocks for additional baud rates are also available from IC4 as well. The table below gives the baud rate and respective output pin number of IC4.
BAUD RATE | MP-A2 IC4 pin |
75 | 9 |
200 | 6 |
1800 | 15 |
2400 | 3 |
3600 | 16 |
4800 | 2 |
7200 | 17 |
9600 | 1 |
To use the selected clock, run an insulated jumper between the specified pin and pin 13 of IC10 on the MP-A2 board. Run another insulated jumper between pin 12 of IC10 and either the UD1 or UD2 bus connections points at the connector edge of the MP-A2 circuit board. IC10 is a low power TTL buffer which must be inserted between the baud rate clock generator and the mother board bus. Since user defined lines UD1 and UD2 are carried on just the 50-pin main board bus and lines UD3 and UD4 are carried on just the 30-pin interface board, it will be necessary to jumper two of the buses together to provide the selected baud rate clock on the interface card bus. Each serial interface card to be operated with the selected baud rate clock will have to be jumpered so its clock is acquired from the selected user defined line rather than one of the five original baud rate clocks already present.
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