[aprssig] Re: D700A gps interface problem

Stephen H. Smith WA8LMF2 at aol.com
Wed Jul 21 03:34:39 EDT 2004

My guess about this is that the new Deluo units probably either:

1)  Need the incoming RS-232 data line ( relative to the GPS ) asserted 
in order to make it turn on.  This seems to be an increasingly common 
feature in mouse-type GPS units to eliminate the need for a power 
switch.  The RS Digitraveller was the first unit of this type 
encountered on this list.  The Digitraveller needs to see either + or - 
RS-232 level from the device it is connected to (PC, D700, TinyTrak, 
etc) before it starts.  The default behavior of the TinyTrak (and I 
think also the D700 unless waypoints are being uploaded to a GPS device) 
is to have the outgoing pin of the GPS port inactive (0 volts).   I had 
to provide a pullup resistor to make the TT work with the Digtraveller.

I wonder if the new Kenwood is setting the outgoing GPS serial port line 
to tri-state inactive instead of driving it to either - or + RS-232 
level, denying the GPS the turnon signal it needs.  Perhaps the older 
D700 is activating the outgoing line.


2)  The Deluo needs RS232 handshaking lines asserted to turn on.  When 
it is plugged into the PC to test with Visual GPS, etc, all the 232 pins 
are asserted by the PC serial port.  When you connect to the D700 GPS 
port, you only have a 3-wire basic serial port connection with TXD, RXD 
and GND/COMMON.  The handshaking lines are left floating unless you make 
null-modem-type cross-connects in the male DB9 on the 
DB9-to-2.5MM-stereo-miniplug cable going into the Kenwood.

The standard DB9 wiring to assert local-handshake foldback are:

   Pins 1(CD), 4(DTR) and 6(DSR) connected together

   Pins 7(RTS) and 8(CTS) connected together

[ This are just cross connections on the back of the connector; they 
don't leave the plug at all. ]

The three lines that actually leave the DB9 connector to go to the 
device at the other end are:

   Pin 2 TX Data wire to far end

   Pin 3 RX Data wire to far end

   Pin 5 Common/GND wire to far end

Stephen H. Smith                   wa8lmf (at)  aol.com
Home Page:                            http://wa8lmf.com

More information about the aprssig mailing list