hsplab@ecsvax.UUCP (01/08/84)
Information about the MITS SIO board is available in the
S-100 Bus Handbook by Dave Bursky. Unfortunately, I do not
have information about the jumpers. Basically the board must
be set up to occupy 4 ports in the IO space of the 8080. The
even ports are for control and the odd ports are for data.
There are two ports on the board. The board uses the Motorola
6850 UARTS and data can be obtained from those data sheets.
Pins 3 and 4 on the 6850 are the receive and transmit clocks
going into the chips. The initial setup must be done with
jumpers and a counter on those pins will tell you the initial
baud rate, the measured rate divided by 16. The following is
an outline of the information accepted by the control port for
the purposes of initializing the 6850:
Bits 5,6,7 control the interrupt circuits. Since most
CPM software handle this poorly, especially for
Mits circuits, they should be set to all zeros
to disable them.
Bits 2,3,4 control the parity/frame size/stop bits
bit 4 = 0 7 data bits; bit 4=1 8 data bits
bit 3 = 0 2 stop bits; bit 3=1 1 stop bit
bit 2 = 0 even parity; bit 2=1 odd parity
exception: bits 4,3,2 = 100 8 bits, 2 stop bits, no parity
101 8 bits, 1 stop bit, no parity
Bits 1,0 00 clock divide by 1
01 clock divide by 16
10 clock divide by 64
11 master reset
Since the clock is 16 time the baud rate, the effect of a divide
by 16 is to divide the baud rate by 2; divide by 64 divides the
baud rate by 4. The initial clocks are set to one of eight rates
between 110 and 9600. I do not think that there will be any
problems with a 1200 / 300 baud scheme being proposed.
David Chou
University of North Carolina, Chapel Hill
...{mcnc,unc,duke}!ecsvax!hsplab