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?

[Pops Racer]

I did some digging to find out why the IN 020 was giving me 377 (all ones).

I thought there might be a problem with the 8T97 buffers and the SINP signal. So out with the cheapo 10MHz scope (that was a good investment for 150 bucks) and start probing. Hmmm - SINP working on IC S - all good.

But the OUT 021 was working perfectly. hmmm - some overlap on the 8T97 chips between Data In and Data Out - maybe it was the chip enable coming out of IC P (7400) - lets go check pin 8 on IC P - The only pin on the whole board that I did not solder!!! arrrgh!

Out with the card - solder pin 8 on IC P. Card back in, hook up computer to serial. Develop more finger calluses toggling in the echo program. Voila! It works! Now on to loading Basic. I've got 5K installed, what will happen with 4K basic? I guess the memory space is set by the loader? Or is is hardcoded in the basic tape?

Thanks for all the help

Cheers
Kelly

[Grant Stockly]

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