[ntp:questions] Re: RS-422 Cards

mike michael.no.spam.cook at wanadoo.fr
Tue May 3 16:20:26 UTC 2005

Stewart Pelegan wrote:
> I've found out that in order to use the customer's GPS source on-site, I 
> will have to interface with a 25 pin RS-422 port.  The workstation 
> receiving the GPS data and running the ntp daemon only has a 9 pin RS-232 
> port.  I'd like to test my RS-422/232 converter on some RS-422 source, but 
> I can't seem to find any...other than going to the customer's site.  Does 
> anyone know where I can get an RS-422 PCI card with a DB25 port?  When I 
> go to the local CompUSA and Radio Shack, all I get is puzzled looks. 
> Thanks.
  If you just want to test the converter, using another converter back 
to back would probably be easiest. Do you have enough  pins? RS422 is a 
4 wire differential standard. Looking at the majority of converters on 
the market, they will have 2 Tx/Rx pair terminals on the RS422 side, 
which will be ok for receiving NMEA or private time protocol messages 
and for sending control data, but if you want to use any PPS output on 
the DB25 you need another  RS422 input converter to connect to the DCD 
line ! If you don't have it already, ask the owner of the GPS to give 
you a pinout of the DB25.

Once you have that you can make a cable up.
According to a googled doc the standard R422 connector (RS530) pinout 
for Tx/Rx is:

Pin Number   Input/Output   Description
2(A), 14(B)  Output         RS-422/530 TxD - GPS receiver output
3(A), 16(B)  Input          RS-422/530 RxD - GPS receiver input

but the PPS could be anywhere . RS530 has DCD pair on pins 8/10
> Stewart Pelegan
> Computer Sciences Corporation
> 301.921.3206
> Fax: 301.921.0985
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