DACIA - Dual 6850/ACIA - Wire-wrapped

This homebrew dual serial port board for the SS-30 bus provides:

When I upgraded my SwTPc system from the MP-A2 6800 CPU board to the MP-09A 6809 CPU board, I needed a new serial card. The MP-09A's SBUG-E 1.5 monitor didn't support the MP-C serial card with its bit-banged 6820/PIA, only ones that used the 6850/ACIA chip. I modified my motherboard to support extended (20-bit) addresses, which meant the baud rate clock generator on the MP-09A had to be removed, leaving the 8 I/O slots without the 5 clock signals. As a result, a SwTPc MP-S card couldn't be used without providing another source of baud rate clocks.

The newer SwTPc motherboards had an MP-ID card that provided the baud rate clocks. Newer GIMIX motherboards had a slot for a separate baud rate generator board. I didn't know how other owners of SwTPc systems provided the baud rate clocks for their serial port cards when they upgraded to the 6809 and modified their older MP-B motherboards to enable extended (20-bit) addresses. Although I did later find mention that SwTPc offered a baud rate generator card that plugged into the SS-30 bus, I have never seen one.

I decided to solve both issues by building my own serial port card with a 6850/ACIA and its own baud rate clock generator. As a bonus, it would have not one, but two serial ports on the one card. All six RS-232 lines are supported and present on the I/O connector: Tx Data, Rx Data, RTS, CTS, DCD, GND. Wiring connects the 12-pin Molex connector with two DB-25 connectors on the rear panel. (Recently I rewired this to use more modern DE-9 connectors.)

However, using this card with a 6800 CPU board and SwTPc's SWTBUG monitor ROM would require modifying the SWTBUG code. Apparently having two 6850/ACIA chips in the same I/O slot confuses SWTBUG's automatic detection of MP-C vs. MP-S cards. But I never used this card with the 6800.

(Click on a picture for a larger version.)

icon to link to photo of top side of DACIA board icon to link to photo of angled view of top side of DACIA board icon to link to photo of angled view of bottom side of wire-wrapped DACIA board
Pictures of my dual-port serial card. (497-824KB .jpg)

Last revised 2024-May-13 11:15 PDT.
Copyright 2021- David C. Wiens.

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