Altair Kit #33 Arrives

[Geoff Harrison]

Originally Posted by Pops Racer

Now trying to figure out how to connect 2SIO to PC. I suspect both circuits are DTE and so must be 'crossed-over' (null-modem) TX -> RX, etc. Do you use DTR and RTS?

If you wire the port as per the MITS manual you end up with an odd hybrid DTE/DCE port. Tx and Rx are set up as though it is a DCE, but it uses the control lines as though it is a DTE. The 6850 requires CTS and DCD to be asserted, so you either have to tie them high in your cable, or give up on hardware handshaking and tie pins 23 & 24 to ground on the 6850 (remember, the signals are inverted on the board), in which case a straight cable will work fine using just the data lines and ground.

Geoff.

[Pops Racer]

Originally Posted by Geoff Harrison

If you wire the port as per the MITS manual you end up with an odd hybrid DTE/DCE port. Tx and Rx are set up as though it is a DCE, but it uses the control lines as though it is a DTE. The 6850 requires CTS and DCD to be asserted, so you either have to tie them high in your cable, or give up on hardware handshaking and tie pins 23 & 24 to ground on the 6850 (remember, the signals are inverted on the board), in which case a straight cable will work fine using just the data lines and ground.

Geoff.

Cool - I have wired it the way that Grant descibes and when I run the echo test I get continuous spaces on the terminal and nothing shows when I type.

Have the board strapped for I/O 20/21 octal. I tried changing the input from port 21 to input from sense switches (port 377) and voila! the transmit works great.

The receive does not work - When single stepping, the IN 020 gets a 377 octal - why would the input from the control register return all 1s?

[Grant Stockly]

Did you have any issues with mounting the motherboard? Where are the pictures?