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eed30b Bob Green 2026-03-12 09:34:11
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# Board Features
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The sbc-3 board contains the following:
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a6a5a9 Bob Green 2026-03-27 09:57:01
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- Two banks of static ram. Each bank can take either 4x512KB AS6C4008 or (if you like soldering SMDs) 4x2MB CY62167ELL. The BIOS will autodetect the amount of memory present. Max memory possible in the two banks is therefore 16MB.
eed30b Bob Green 2026-03-12 09:34:11
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- XR68C681 Duart. Two independent serial ports. _See the note below about the PS/2 keyboard and mouse._
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- CompactFlash interface
acf411 Bob Green 2026-05-18 12:18:57
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- MC68230 PI/T. Provides two banks of 8-bit I/O and a timer counter, driven by an external 10MHz clock.
eed30b Bob Green 2026-03-12 09:34:11
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- DS1307 Real time clock with battery backup.
7e3127 Bob Green 2026-03-16 18:08:52
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- PS/2 keyboard and mouse interfaces. If you use these, they will tie up the second port on the duart. The PS/2 signals are decoded by an on-board ATMega328 and passed to the main processor via channel B on the duart. Jumpers will need to be set accordingly.
eed30b Bob Green 2026-03-12 09:34:11
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3db9dd Bob Green 2026-03-12 11:22:50
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## Duart
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3c330c Bob Green 2026-04-02 09:46:56
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> [!NOTE]
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> I bought a Motorola MC68681 duart and discovered that it should have been an XR68681 duart. The Motorola part is an older design and can't run at the speeds that the newer chip can. I was able to get it to run, but at 38400 instead of 230400. When you're loading large programs via the serial interface, that makes a *huge* difference, so don't be like me, get the correct chip first time.
3db9dd Bob Green 2026-03-12 11:22:50
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## PI/T
0fcbbd Bob Green 2026-03-12 14:56:30
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The PI/T has three 8-bit ports in total, two of which (ports A and B) are general purpose I/O. The third port (port C) can be configured to present some of the Timer/Counter internals to the outside world.
dd1f03 Bob Green 2026-03-24 15:42:18
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On the sbc-3, two pins of port C (0 and 1) are used to implement a bit-banged `$I^2c$` bus to talk to the on-board real time clock, a Dallas Semiconductors ds1307.
0fcbbd Bob Green 2026-03-12 14:56:30
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4f022c Bob Green 2026-04-02 09:44:51
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#### Links
cd1d60 Bob Green 2026-04-02 09:43:08
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- [An Example](https://people.engr.tamu.edu/rgutier/web_courses/ceg453_s00/l2.pdf) I found of how to program the device and handle the interrupts in C.