>
> 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.
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.
Reply by Jens Hildebrandt●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
Reply by Ralph Malph●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 Stef●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 Anton Erasmus●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 Ralph Malph●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 Ralph Malph●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 Michael Anton●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 Michael Anton●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 jim granville●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?