Serial Interfacing

N

nfk

Senior Member
In the 'Interfacing Circuits' manual section 3 deals with interfacing to a computer and shows a recommended 5v configuration with resistors on the Rx and Tx lines. How important are these? Is this what I should be doing for all my serial comms to external devices? (I'm only using 5v serial devices.) My guess is that they are just for protection rather than anything else.

For example my excellent little AXE033 LCD display works very nicely connected directly to the pins of the PICAXE chip without any series resistors.

Cheers,
Nigel
 
M

MBrej

Member
You only need those resistors when you are interfacing with a computer, as the PC serial port uses -12V to 12V, and these resistors help protect the PIC. If you are using serial to communicate with something that runs off the same power supply such as the LCD screen, the resistors are not needed. However, if you are interfacing to something which runs off a lower voltage such as 3.3V, normally on the wire between the PIC out and device in a potential divider will be needed, alothugh be careful, the resistor arrangement shown between the PIC and the PC is not a potential divider.

Matt
 
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