SIO1 and SIO2 Information

SIO1 and SIO2 are not really separate ports, just separate connectors that can be activated by means of a multiplex command to carry the COM: serial signal. The multiplex port is 144 decimal, 90 hex. You can enable SIO1 with the command

OUT 144,160

within a BASIC program. For SIO2, I am told that you would use

OUT 144,96

although I cannot personally vouch for that, having not tested that myself.

WARNING #1 (from the school of hard knocks--believe me, I wasted an entire weekend on this): The multiplex settings are canceled whenever you enter TELCOM, so if you want to do file transfers, you would need to program your own TELCOM-like utility that addresses port 144 and performs low-level byte transfers. I will be writing such a program myself, so if you want a copy or would like to be a beta tester, please contact me.

WARNING #2 (also from the school of hard knocks): Simply invoking TIME$ in BASIC will reset the multiplex settings, so be sure to check the status of port 144 frequently by polling port 160 as follows:

X=INP(160)
IF X=160 THEN PRINT"Oops, no longer on SIO1."
There may be other BASIC commands like TIME$ that have this same undesirable side effect, so beware.

Finally, the connector you use for SIO1 is a standard RJ45 network plug, but with nonstandard pinouts. Are you trying to connect two NECs together, or are you trying to use SIO1 to communicate to the serial port of a more modern PC?

If you're trying to connect two NECs, here is the method:

Take a standard Category 5 network patch cable (i.e., straight-through cable), with wires 1-8 as follows:

1 = white-orange
2 = orange
3 = white-green
4 = blue
5 = white-blue
6 = green
7 = white-brown
8 = brown

Leave one end of your RJ45 cable just as shown above. Then cut off the other end and use a crimping tool to attach a new plug there, wired as follows:

1 = white-orange
2 = white-green
3 = orange
4 = white-blue
5 = blue

Snip (do not connect) the green, white-brown, and brown wires.

If you would like to buy a pre-made cable, I have made several and could send you one at a reasonable price.

Sincerely,

Michael
http://www.modd.net