PICAXE Intercom

[AllanBertelsen]

I got one 18X serving as master and 08M serving as slave.

Now they work fine talking serin/serout via two lines. I even managed them to use interrupt to trigger communication so they won't have to spent time just listening for serin.
Then I realised, that I need 4 I/O's on the 08M in addition to the communication lines.

I got a spare line on the wire between master and slave. But I can't use this for the fourth I/O on the slave side. 08M has to use all 4 I/O's directly. I was thinking on the possibility to use only on pin for I/O on 08M as they can change direction.

I got a quad NAND gate. I could maybe use the spare line to control direction as a read/write signal.

I was thinking of something like this:
<code><pre><font size=2 face='Courier'>
____
serin / |----------.
--------o| | |
\____|-----. |
| |---- I/O on 08M
serout ____ | |
---------| \ | |
| |o---------.
.---|____/ |
| |
| |
| ____ |
R/W | .-| \ |
-----.-| | |o----.
.-|____/
</font></pre></code>

Do you have any suggestions?

 

[Technical]

Put a resistor between the output of the centre gate and the PICAXE i/o or else you may have problems.


In fact you can do the whole thing just with a resistor. Just connect the 08 pin directly to the 18X input. Then connect the 18X output, via a resistor (e.g. 1k) to the 08 pin.

When the 08M transmits (outputs) the resistor preevents a short between the two outputs.

When the 18X transmits its information is echoed back to the 18X input, but that doesn't matter.

 

[AllanBertelsen]

Aha. That&#8217;s very nice. I will try it at once. Thank you.