Question about AXE026 serial cable

[Sean87]

Hi all,

So I am using AXE026 cable for a while to program my PICAXE chips. But I have a technical question. As far as I know, PC's serial port are working on +/- 15 volts (Correct me if I am wrong please). So does this cable comes with a converter built in to it that reduces this voltage? I know that for connecting this cable to PICAXE I have to use 22k and 10k resistors. But in manual says this resistors are not voltage dividers.

I am asking this because I Am considering using this cable to interact with another device that uses CMOS TTL (according to its datasheet). Is it safe to use this cable?

Thanks.

 

[nick12ab]

The cable does not convert the voltage. The resistors limit the current to a safe level so that the clamping diodes in the PICAXE reduce the voltage to around Vdd+0.3V.

Before using the cable and resistors with something else, you must check the datasheet to see what the maximum current the clamping diodes support to see if you need to use higher value resistors.

 

[Goeytex]

There is no converter built in.

It works because of the Picaxe download circuit that consists of the two resistors AND internal clamping diodes on the Picaxe serin pin. The 22K resistor works in conjunction with an internal clamping diode to clamp the +10 to +15v to Vcc +.3v

You could safely use the cable with the other device if you incorporate EXTERNAL clamping diodes and a current limit resistor. See below