Need help on ‘enhanced’ interface circuit is used on a serial connection

nick12ab

Senior Member
I see. So I can't make PICAXE boards that are compatible with both types of cable - the old serial one and the new USB one?
You can keep the 22k and have the ability to use both logic level and RS232 download cables. The 22k+10k isn't a potential divider - the signal coming from the download cable goes into the 'output' of this potential divider-like resistor setup. The 10k is just a pull-down and the 22k is a current limiter. The clamping diodes inside the PICAXE do the rest.
 

mrburnette

Senior Member
@nick12ab:

Yea, you're right... I had read back too far in the post to where a lots of stuff was being discussed and for some reason, brought that baggage forward when I answered. Thank for setting the answer right.

- Ray

RS232 PICAXE Input.jpg
 
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Andy2No

Member
Ah. Okay. Thanks, Ray and Nick.

Yes, I realised the resistors aren't a potential divider. I wasn't sure how much of a voltage drop there'd be across the 22k resistor due to the input current though... I see page 43 of part 1 of the manual does say to use the same circuit for both cables.

Does the AXE027 USB cable have 5V TTL output levels, as I assumed, or are they higher to make it more like the output of the old serial cable?

Ray,

I hadn't considered the Java applet might just have run out of memory. Mine's almost full most of the time so that could be the reason. I'll have to try it without so many tabs open in the browser, probably in a different browser. I got it to accept a circuit by starting again but giving it a square wave or AC input doesn't seem to do anything. Maybe I'm just missing something.
 
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