Hey guys...
After learning so much from Nigel and this site a few months ago, i've made huge leaps and bounds and have made a few circuits that i'm quite proud of, so firstly thank you
I've now completed the project I primarily started out to do with some major upgrades along the way...
Basically i have a terminal with RFID that is able to distinguish user cards from job sheets and a keypad with LCD acting as terminals for a PC. This is all working great interfacing with a PC via RS232... here is where I need help please...
Im looking at moving to rs485 instead for long distance, but have read so much conflicting info that I'm worse off now than when I started researching it...
1. If I power all terminals from a single power source, I should not need to worry about ground loops and potential difference correct?
2. Can I run the power lines inside the same shielded twisted cable without causing problems? (I figure it shouldn't be a problem since rs485 signals are opposing eachother and will therefore cancel noise)
3. Im confused with the rs485 trancievers... Could some one explain the RE and DE on the chips? How come on most schematics they are connected to one uController pin?
4. I was unable to get the PIC16F877A to work with a 20MHz crystal, I thought 20Mhz was the limit? Must I go down to 19Mhz? It is working on 4Mhz but that limits my bit banging to 4800 over 232 which is very slow...
Thanks
Claudio