RS485/422 to UART , TTL

[amgen]

Has anyone here tried hooking up an RS485 or 422 type device directly to UART pins on a PIC without a converter. I know there is A,B and GND signals with differing polarity related to ground ?

Don
amgen

[Charles Linquis]

I have done it many times. MAX13080E. Why would you need a converter? The MAX parts have logic levels on one side and RS-485 signals (both full and half duplex options) on the other.

[amgen]

I am looking at WizNet810 485 to ethernet module, about $20, and I always try to reduce/eliminate glue-logic. I have been using the wiz710 serial to e-net but the uart output of TX & RX has to be inverted. Thats why I was wondering about hooking directly to the module in-out with no other items on the 485 bus. I think the module has half and full duplex, selectable.

Don

[dhouston]

If you mean Wiz107 & Wiz108, the 108 requires a differential input which you cannot do directly - that's why they make transceiver chips. Why not just use Debug/DebugIn and invert the logic with your Wiz107 serial adapter?

[amgen]

Yes, meant Wiz108 and 107, I don't have a 485 device for testing. But just thinking, differential input only means A>B by 2volts and B>A equals the 1's and 0's, so may be able to use voltage divider resisters on A or B and TX then on other pin for transmit to 485, and to recieve from 485 is just one of the differential outputs and gnd.
I am now using hardware TX and RX from USART and interrupt for both in my program to send and recieve data. Since Debug isn't for interrupts, that would change the whole setup.
The 107 generally works OK but it would hap-hazardly(?) erase its flash IP settings making it inoperable until reprogramming the flash, but it seems better since loading newer version of operating program from WIZ.
I also saw the $30 802.11 WIZ module a few days ago and would like to try that too.

Don

[dhouston]

What PIC? On some (e.g. 16F88), you can access inputs/outputs of both comparators and use them as inverters.

However, I haven't used the Wiz107SR module you are using, but most serial-to-ethernet modules intended for interfacing with a µC use positive logic. And, the datasheet for the Wiz107SR indicates you should make direct connections with no need to invert. Connect module TXD to PIC RX and module RXD to PIC TX. You may need to jumper RTS & CTS if you are not using flow control (seldom needed for this) but this may be handled in the configuration of the Wiz107SR