6809 based DSA card
I didn't design this board but was responsible for most of the software
and the debugging of the hardware. The board uses a 6844 DMA controller
to provide full duplex comms to a pair of HDLC chips at speeds of up to
76K baud. This required the operation of the chip in 4 DMA channel
mode. During the processing we found undocumented problems with both
the 6809E and the 6844 which were confirmed by Motorola in the USA.
These problems where worked around by additional hardware and switching
to a Hitachi processor (6809 clone). In addition to the DMA performed
on the board itself there is a FIFO interface to the ISA bus and the PC
does DMA transfers to and from this FIFO. This board is now used to run
all of the telephone betting terminals in the Wellington region and all
race tracks in the north island. The board can handle up to 64
terminals and up to four of these board can be fitted to an OS2 based
PC. The DSA card is also covered in the software section.
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