Boy, I thought it was tough finding an I2C port expander chip that fit all my requirements. I am looking for an RS485 tranceiver that I can use along with an RS232 chip to allow either protocol through the same pins. But I can't find an acceptable chip anywhere. This was discussed a few weeks ago, but I don't think anyone mentioned any part numbers that were compatible. I think I can find an RS232 chip that will tristate the outputs, but I can not find a full duplex RS422/RS485 chip that is +- 15 volt tolerant. Anyone actually done this before?
RS485 with +-15V common mode
Started by ●January 23, 2004
Reply by ●January 23, 20042004-01-23
Ralph Malph wrote:> Boy, I thought it was tough finding an I2C port expander chip that fit > all my requirements. I am looking for an RS485 tranceiver that I can > use along with an RS232 chip to allow either protocol through the same > pins. But I can't find an acceptable chip anywhere. > > This was discussed a few weeks ago, but I don't think anyone mentioned > any part numbers that were compatible. I think I can find an RS232 chip > that will tristate the outputs, but I can not find a full duplex > RS422/RS485 chip that is +- 15 volt tolerant. > > Anyone actually done this before?Yes, Maxim. ( and I think Linear too ?)
Reply by ●January 23, 20042004-01-23
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 "Ralph Malph" <noone@yahoo.com> wrote in message news:4011AF00.A6989CA3@yahoo.com...> Boy, I thought it was tough finding an I2C port expander chip that fit > all my requirements. I am looking for an RS485 tranceiver that I can > use along with an RS232 chip to allow either protocol through the same > pins. But I can't find an acceptable chip anywhere. > > This was discussed a few weeks ago, but I don't think anyone mentioned > any part numbers that were compatible. I think I can find an RS232 chip > that will tristate the outputs, but I can not find a full duplex > RS422/RS485 chip that is +- 15 volt tolerant. > > Anyone actually done this before?
Reply by ●January 23, 20042004-01-23
Remember that full duplex RS485 will require 4 pins, plus a ground pin, whereas RS232 requires 2 pins, plus a ground pin. Mike Anton "Ralph Malph" <noone@yahoo.com> wrote in message news:4011AF00.A6989CA3@yahoo.com...> Boy, I thought it was tough finding an I2C port expander chip that fit > all my requirements. I am looking for an RS485 tranceiver that I can > use along with an RS232 chip to allow either protocol through the same > pins. But I can't find an acceptable chip anywhere. > > This was discussed a few weeks ago, but I don't think anyone mentioned > any part numbers that were compatible. I think I can find an RS232 chip > that will tristate the outputs, but I can not find a full duplex > RS422/RS485 chip that is +- 15 volt tolerant. > > Anyone actually done this before?
Reply by ●January 24, 20042004-01-24
Michael Anton wrote:> > Remember that full duplex RS485 will require 4 pins, plus a ground pin, > whereas RS232 requires 2 pins, plus a ground pin.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.
Reply by ●January 24, 20042004-01-24
Michael Anton wrote:> > 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.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.
Reply by ●January 24, 20042004-01-24
On Fri, 23 Jan 2004 18:32:16 -0500, Ralph Malph <noone@yahoo.com> wrote:>Boy, I thought it was tough finding an I2C port expander chip that fit >all my requirements. I am looking for an RS485 tranceiver that I can >use along with an RS232 chip to allow either protocol through the same >pins. But I can't find an acceptable chip anywhere. > >This was discussed a few weeks ago, but I don't think anyone mentioned >any part numbers that were compatible. I think I can find an RS232 chip >that will tristate the outputs, but I can not find a full duplex >RS422/RS485 chip that is +- 15 volt tolerant. > >Anyone actually done this before?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
Reply by ●January 24, 20042004-01-24
In comp.arch.embedded, Ralph Malph <noone@yahoo.com> wrote:>that will tristate the outputs, but I can not find a full duplex >RS422/RS485 chip that is +- 15 volt tolerant. >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
Reply by ●January 25, 20042004-01-25
Stef wrote:> > In comp.arch.embedded, > Ralph Malph <noone@yahoo.com> wrote: > >that will tristate the outputs, but I can not find a full duplex > >RS422/RS485 chip that is +- 15 volt tolerant. > > > 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.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...
Reply by ●January 26, 20042004-01-26
Ralph Malph wrote:> Boy, I thought it was tough finding an I2C port expander chip that fit > all my requirements. I am looking for an RS485 tranceiver that I can > use along with an RS232 chip to allow either protocol through the same > pins. But I can't find an acceptable chip anywhere. > > This was discussed a few weeks ago, but I don't think anyone mentioned > any part numbers that were compatible. I think I can find an RS232 chip > that will tristate the outputs, but I can not find a full duplex > RS422/RS485 chip that is +- 15 volt tolerant. > > Anyone actually done this before?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
