Welch Allyn Scanners

Had a project to do with a barcode scanner IT3800 and a basic module in a SLC5/04. I wrote a bit of basic code for the basic module, so that when I scan a barcode the information is transferred to the SLC through port 2 of the basic module. I was using a type 12 IT3800 scanner and couldn't get the barcode information in to the SLC, but when I connected the scanner to the serial port of my pc, I could scan the barcode in to procomm no problems.

I then noticed that we have 2 types of IT3800 scanner on site, a type 12 and a type 13...Doh, the type 13 scanner worked straight away when i connected it to the basic module. I've checked the spec sheets of the 2 types of scanner and can't see any obvious differences, can anyone offer any help or an explanation.

One of my colleagues says that it is because there are 2 types of RS232, 1 that uses voltage for its signals, and 1 that uses current???.

Any help appreciated

Cheers
Sparky

sparky64 said:

One of my colleagues says that it is because there are 2 types of RS232, 1 that uses voltage for its signals, and 1 that uses current???.

Sparky

Click to expand...

Naaaa, he's goofy.

The difference between the two types is that the 12 uses TTL level (0-5v ish)serial signals and the 13 uses true RS-232 levels (-15 max to +15 max). I don't know the exact voltage levels for the 13, but from what you say, it looks like it goes negative.


Here's the defined voltage levels vs signals for RS-232 :

An output voltage is:
positive if it is from +5 to +15 volts
negative if it is from -5 to -15 volts
undefined if it is from -5 to +5 volts


An input voltage is:
positive if it is from +3 to +15 volts
negative if it is from -3 to -15 volts
undefined if it is from -3 to +3 volts



Many serial ports will work with the TTL levels, some will not. Guess you found one that doesn't.

Thanks for the reply, at least now i know why.

Sparky