RS485 with +-15V common mode

Yes, Maxim. ( and I think Linear too ?)

Take a look at LTC1387.

BTW +-15V tolerant is not specifically within the standard RS485 spec, which is -7V to +12V, so it may not be easy to find.

Mike Anton

Remember that full duplex RS485 will require 4 pins, plus a ground pin, whereas RS232 requires 2 pins, plus a ground pin.

Mike Anton

Actually, I will be using a full 8 pins plus ground so that the RS-422 has Tx, Rx and clock either in or out. The standard PC RS232 interface uses 8 signals and ground although I will likely have 4 in and 4 out while the PC uses 5 in and 3 out. With 4 each way it will be short one of each when talking to a PC (DCE) or acting like a PC (DTE) while with

5/3 it will be short two handshakes when doing one or the other.

Thanks for the info. I am aware of the spec, but I have seen some devices that have +-15 volt tolerance or even +25 -20 volts. But they are RS-485 either half duplex (so they won't do RS422) or no enables (so they can't share outputs with the RS232 device).

I have seen the LTC parts. In fact the design was using an LTC1334. But this part is $6 and they won't come down. Sipex and Maxim have similar parts at the same price. I am trying to save a few bucks, but not take up a lot of space.

I may give up on the multiprotocol and use RS232 with an external adapter.

Isnt the RS423 spec a sort of combination of RS422 and RS232 ? So that a RS423 buffer could be used in either a RS232 environmnet or RS422 environment ?

Regards Anton Erasmus

Linear's LT1785 and LT1791 are +/- 60V tolerant. Both have driver enable an receiver enable. The LT1785 is pin compatible with the 75176 and the LT1791 can be used full-duplex.

--
Stef            (remove caps, dashes and .invalid from e-mail address to reply)

A boy gets to be a man when a man is needed.
		-- John Steinbeck

Seems this is just not going to work. I would need two of these along with an RS-232 chip. At $2.50+ each the total cost is more than the single chip approach and also a lot more board space.

Oh well...

I just remember the MAX3160/3161. You can switch this part between RS232 (

2Rx/2Tx) , Full-Duplex RS485 or Half-Duplex RS485. RS232 and RS485 mode use the same pins and according to the datasheet they allow +/-25V input voltage.

HTH, Jens

the

Yes, Sipex and Linear Tech also make this sort of part. But they all charge a lot for them. That is why I am looking for a two chip (three actually) solution.