Diode mixing serial comms

Having some problems here, trying to diode-mix serial outputs onto a common bus.

When directly connected from one picaxe to another, it works beautifully.
If I put a 914 diode on the output pin, anode to the output pin, cathode to the bus, and connect a PC between GND and the diode cathode, that also works beautifully.
When I connect the cathode end of the diode to the other picaxe serin, it ignores any and all commands totally - it's like they simply are not there.

How come?

I will try some more experimentation...

ADITIONAL:
Hmmmmmmmmm.
Interesting...

If I put the PC cable in parallel with the connection to the 2nd(receiving) picaxe, across the diode cathode and GND, both the PC terminal AND the receiving picaxe work - if I remove the serial cable to the computer, the receiving picaxe ignores the messages again...

Will try a 10k pull up then pull-down resistor and see what happens.

MORE ADDITIONAL:
Wow - things are getting interesting.


If I put a 10k pull-down resistor between the 914 cathode and deck(GND), and connect the 2nd receiving picaxe across that(essentially connecting the receiving picaxe's input across the 10k to deck, fed from the 914 on the ouput of the 1st picaxe), then everything works beautifully.

Problem is, I can't put one on each node, or the total line resistance will change.
Could I get away with one single pull-down at the receiving end, do you think?
More experimentation...

You should be able to get away with a single pull-down on the bus to 0V with all PICAXE inputs reading from the bus. Best thing is to try it.

It shouldn't be necessary to have a pull-down on each input, but you can do that without the parallel resistance becoming a problem. If 10K works for one PICAXE, use two 20K's for two, 33K for three, etc. Ohms Law for R's in parallel.

The pull-down R value isn't particularly critical as it's just to stop the bus floating whan all outputs to the bus via diodes are zero. The PC serial port usually has a pull-down R built-in, PICAXE inputs don't.