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Re: Serial Communication

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  • ruggb66
    I m not familiar with this problem, BUT the comm interface is actually THREE wires Rx Tx Ground so communication can be full duplex, but I don t think it is.
    Message 1 of 7 , Oct 1, 2007
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      I'm not familiar with this problem, BUT

      the comm interface is actually THREE wires
      Rx
      Tx
      Ground

      so communication can be full duplex, but I don't think it is.
      The format NMEA or GARMIN simply reflects the data format this
      exchange has and also what data can be obtained from the GPS.

      In your case only Rx and Ground are used
      Rx = NMEA+
      Ground = NMEA-

      This is actually a RS422 balanced connection, not RS232. But it workes
      with + to Rx and - to ground.

      The VHF is most likely looking for 4800 baud in NMEA format.

      Since u didn't specify I can only ass-u-me that u are not connecting
      the ground to the NMEA-.



      --- In GarminGPSMAP60C_60CS@yahoogroups.com, Gary Turner
      <g.turner@...> wrote:
      >
      > I'm only guessing/thinking - but I would have thought that NMEA
      would be constant transmit-only, but that the default garmin protocol
      could be question/response.
      >
      > Was the GPS in NMEA mode, or Garmin mode?
      >
      > Being 2-wire only, the comms must use software handshake. I guess
      your radio must be able to simply suck up all the data. There would be
      no way otherwise to send any XON/XOFF's.
      >
      > ----- Original Message -----
      > From: frans.plugge
      > To: GarminGPSMAP60C_60CS@yahoogroups.com
      > Sent: Friday, September 28, 2007 7:55 PM
      > Subject: [GarminGPSMAP60C_60CS] Serial Communication
      >
      >
      > Hi,
      >
      > When I connect my GPSMAP 60CS via the serial connection to my PC with
      > only the Tx-line connected to the Rx of the PC, there is no
      > communication. Only when I also connected the Rx of the GPS to the Tx
      > of the PC does the communication start. I'm trying to connect the GPS
      > to a device (VHF radio with DSC), which only receives NMEA-data and
      > therefore only has a Rx line.
      > Is anyone familiar with this problem (I'm using firmware 4.0)?
      >
      > Kind regards,
      > Frans
      >
    • frans.plugge
      Thank you all for your reactions. Let me elaborate it little more on my findings. I ve checked the interface setting and it was set to NMEA in/out at 4800
      Message 2 of 7 , Oct 2, 2007
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        Thank you all for your reactions. Let me elaborate it little more on
        my findings.

        I've checked the interface setting and it was set to NMEA in/out at
        4800 baud. With a normal serial cable for the GPSMAP 60CS I
        established normal communication between the GPS and the PC (via
        Hyperterminal). All the NMEA sentences came through perfectly.
        Then I made a cable with only three wires: Rx, Tx and Ground (pins
        2,3 and 5 on both sides). I used this cable between the standard
        serial cable and the PC and again I established normal communication
        (even tested it with a cross cable between two PC with
        Hyperterminal).
        So finally I tested the situation, where the receiving unit (in this
        case the PC) only had a Rx and Ground wire. Therefore I disconnected
        the Tx wire in the experimental wire. And communication stopped. As
        soon as I connected it again, communication resumed. For good
        measure I also disconnected the Rx wire (no surprise there, no
        comm.) and disconnected the ground wire (again no comm., no
        surprise).
        When I use the same experimental cable with only a Rx and Ground
        cable with my old Etrex unit, it works perfectly. So I'm inclined to
        assume it must be the firmware of the GPSMAP 60CS. I have installed
        version 4.20 which did not solve the problem.

        Frans

        --- In GarminGPSMAP60C_60CS@yahoogroups.com, "ruggb66" <ruggb66@...>
        wrote:
        >
        > I'm not familiar with this problem, BUT
        >
        > the comm interface is actually THREE wires
        > Rx
        > Tx
        > Ground
        >
        > so communication can be full duplex, but I don't think it is.
        > The format NMEA or GARMIN simply reflects the data format this
        > exchange has and also what data can be obtained from the GPS.
        >
        > In your case only Rx and Ground are used
        > Rx = NMEA+
        > Ground = NMEA-
        >
        > This is actually a RS422 balanced connection, not RS232. But it
        workes
        > with + to Rx and - to ground.
        >
        > The VHF is most likely looking for 4800 baud in NMEA format.
        >
        > Since u didn't specify I can only ass-u-me that u are not
        connecting
        > the ground to the NMEA-.
        >
        >
        >
        > --- In GarminGPSMAP60C_60CS@yahoogroups.com, Gary Turner
        > <g.turner@> wrote:
        > >
        > > I'm only guessing/thinking - but I would have thought that NMEA
        > would be constant transmit-only, but that the default garmin
        protocol
        > could be question/response.
        > >
        > > Was the GPS in NMEA mode, or Garmin mode?
        > >
        > > Being 2-wire only, the comms must use software handshake. I guess
        > your radio must be able to simply suck up all the data. There
        would be
        > no way otherwise to send any XON/XOFF's.
        > >
        > > ----- Original Message -----
        > > From: frans.plugge
        > > To: GarminGPSMAP60C_60CS@yahoogroups.com
        > > Sent: Friday, September 28, 2007 7:55 PM
        > > Subject: [GarminGPSMAP60C_60CS] Serial Communication
        > >
        > >
        > > Hi,
        > >
        > > When I connect my GPSMAP 60CS via the serial connection to my
        PC with
        > > only the Tx-line connected to the Rx of the PC, there is no
        > > communication. Only when I also connected the Rx of the GPS to
        the Tx
        > > of the PC does the communication start. I'm trying to connect
        the GPS
        > > to a device (VHF radio with DSC), which only receives NMEA-
        data and
        > > therefore only has a Rx line.
        > > Is anyone familiar with this problem (I'm using firmware 4.0)?
        > >
        > > Kind regards,
        > > Frans
        > >
        >
      • ruggb66
        OK u made me work for this one, BUT I have the solution. I connected my 60 to my scope, and indeed there is no signal on the Tx line. So what can be the
        Message 3 of 7 , Oct 3, 2007
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          OK u made me work for this one, BUT I have the solution.

          I connected my 60 to my scope, and indeed there is no signal on the Tx
          line. So what can be the problem. Well, I guess this is Garmin's idea
          of a joke because I see no need for this configuration unless it is
          used for reason three below.

          Anyway, since the Tx line of the Garmin is actually transmit data then
          this device is considered a DCE. But the Tx line of the PC should
          actually be its RECEIVE line. I bet it isn't. therefore it doesn't
          conform to RS-232 spec and you can't tell which is DCE and which is
          DTE that way. That BS is why this is so confused.

          They have configured this, I guess u want the answer huh?

          they have configured the Rx line to tell them that the unit is
          connected. It is a combination Rx and DTR (Data Terminal Ready) line.
          OR they could be using it as an RTS (Request To Send) line. OR even
          funnier (this is reason 3), they could be using it as power for the
          communication circuit. Now this is where that previous BS becomes
          important.

          In order to know which line to connect to the Rx line to make this
          work you need to know what kind of device DCE or DTE you are
          connecting it to. Because on a DCE, DTR and RTS are inputs. The are
          outputs (and have voltage on them) if it is a DTE. Or you can use a
          voltmeter.

          To make the Garmin work you need to connect the Rx line to a positive
          voltage. Anywhere from 3v up should do it. I don't know what the limit
          is but I would assume 12v is safe because the RS-232 spec calls for
          operation at +- 15v.

          For ease of connection measure the volts on other pins of the rcvr.
          If it is a DB9, pin 4 DTR or pin 6 RTS should be positive. It will be
          on a PC because a PC IS a DTE.

          BTW, I DID verify this by connecting about 4 volts to my unit.

          have fun.



          --- In GarminGPSMAP60C_60CS@yahoogroups.com, "frans.plugge"
          <frans.plugge@...> wrote:
          >
          > Thank you all for your reactions. Let me elaborate it little more on
          > my findings.
          >
          > I've checked the interface setting and it was set to NMEA in/out at
          > 4800 baud. With a normal serial cable for the GPSMAP 60CS I
          > established normal communication between the GPS and the PC (via
          > Hyperterminal). All the NMEA sentences came through perfectly.
          > Then I made a cable with only three wires: Rx, Tx and Ground (pins
          > 2,3 and 5 on both sides). I used this cable between the standard
          > serial cable and the PC and again I established normal communication
          > (even tested it with a cross cable between two PC with
          > Hyperterminal).
          > So finally I tested the situation, where the receiving unit (in this
          > case the PC) only had a Rx and Ground wire. Therefore I disconnected
          > the Tx wire in the experimental wire. And communication stopped. As
          > soon as I connected it again, communication resumed. For good
          > measure I also disconnected the Rx wire (no surprise there, no
          > comm.) and disconnected the ground wire (again no comm., no
          > surprise).
          > When I use the same experimental cable with only a Rx and Ground
          > cable with my old Etrex unit, it works perfectly. So I'm inclined to
          > assume it must be the firmware of the GPSMAP 60CS. I have installed
          > version 4.20 which did not solve the problem.
          >
          > Frans
          >
          > --- In GarminGPSMAP60C_60CS@yahoogroups.com, "ruggb66" <ruggb66@>
          > wrote:
          > >
          > > I'm not familiar with this problem, BUT
          > >
          > > the comm interface is actually THREE wires
          > > Rx
          > > Tx
          > > Ground
          > >
          > > so communication can be full duplex, but I don't think it is.
          > > The format NMEA or GARMIN simply reflects the data format this
          > > exchange has and also what data can be obtained from the GPS.
          > >
          > > In your case only Rx and Ground are used
          > > Rx = NMEA+
          > > Ground = NMEA-
          > >
          > > This is actually a RS422 balanced connection, not RS232. But it
          > workes
          > > with + to Rx and - to ground.
          > >
          > > The VHF is most likely looking for 4800 baud in NMEA format.
          > >
          > > Since u didn't specify I can only ass-u-me that u are not
          > connecting
          > > the ground to the NMEA-.
          > >
          > >
          > >
          > > --- In GarminGPSMAP60C_60CS@yahoogroups.com, Gary Turner
          > > <g.turner@> wrote:
          > > >
          > > > I'm only guessing/thinking - but I would have thought that NMEA
          > > would be constant transmit-only, but that the default garmin
          > protocol
          > > could be question/response.
          > > >
          > > > Was the GPS in NMEA mode, or Garmin mode?
          > > >
          > > > Being 2-wire only, the comms must use software handshake. I guess
          > > your radio must be able to simply suck up all the data. There
          > would be
          > > no way otherwise to send any XON/XOFF's.
          > > >
          > > > ----- Original Message -----
          > > > From: frans.plugge
          > > > To: GarminGPSMAP60C_60CS@yahoogroups.com
          > > > Sent: Friday, September 28, 2007 7:55 PM
          > > > Subject: [GarminGPSMAP60C_60CS] Serial Communication
          > > >
          > > >
          > > > Hi,
          > > >
          > > > When I connect my GPSMAP 60CS via the serial connection to my
          > PC with
          > > > only the Tx-line connected to the Rx of the PC, there is no
          > > > communication. Only when I also connected the Rx of the GPS to
          > the Tx
          > > > of the PC does the communication start. I'm trying to connect
          > the GPS
          > > > to a device (VHF radio with DSC), which only receives NMEA-
          > data and
          > > > therefore only has a Rx line.
          > > > Is anyone familiar with this problem (I'm using firmware 4.0)?
          > > >
          > > > Kind regards,
          > > > Frans
          > > >
          > >
          >
        • ruggb66
          SORRY pin 7 is RTS not pin 6 - that is DSR. If it has voltage on it then the unit is a DCE.
          Message 4 of 7 , Oct 3, 2007
          • 0 Attachment
            SORRY pin 7 is RTS not pin 6 - that is DSR. If it has voltage on it
            then the unit is a DCE.


            --- In GarminGPSMAP60C_60CS@yahoogroups.com, "frans.plugge"
            <frans.plugge@...> wrote:
            >
            > Thank you all for your reactions. Let me elaborate it little more on
            > my findings.
            >
            > I've checked the interface setting and it was set to NMEA in/out at
            > 4800 baud. With a normal serial cable for the GPSMAP 60CS I
            > established normal communication between the GPS and the PC (via
            > Hyperterminal). All the NMEA sentences came through perfectly.
            > Then I made a cable with only three wires: Rx, Tx and Ground (pins
            > 2,3 and 5 on both sides). I used this cable between the standard
            > serial cable and the PC and again I established normal communication
            > (even tested it with a cross cable between two PC with
            > Hyperterminal).
            > So finally I tested the situation, where the receiving unit (in this
            > case the PC) only had a Rx and Ground wire. Therefore I disconnected
            > the Tx wire in the experimental wire. And communication stopped. As
            > soon as I connected it again, communication resumed. For good
            > measure I also disconnected the Rx wire (no surprise there, no
            > comm.) and disconnected the ground wire (again no comm., no
            > surprise).
            > When I use the same experimental cable with only a Rx and Ground
            > cable with my old Etrex unit, it works perfectly. So I'm inclined to
            > assume it must be the firmware of the GPSMAP 60CS. I have installed
            > version 4.20 which did not solve the problem.
            >
            > Frans
            >
            > --- In GarminGPSMAP60C_60CS@yahoogroups.com, "ruggb66" <ruggb66@>
            > wrote:
            > >
            > > I'm not familiar with this problem, BUT
            > >
            > > the comm interface is actually THREE wires
            > > Rx
            > > Tx
            > > Ground
            > >
            > > so communication can be full duplex, but I don't think it is.
            > > The format NMEA or GARMIN simply reflects the data format this
            > > exchange has and also what data can be obtained from the GPS.
            > >
            > > In your case only Rx and Ground are used
            > > Rx = NMEA+
            > > Ground = NMEA-
            > >
            > > This is actually a RS422 balanced connection, not RS232. But it
            > workes
            > > with + to Rx and - to ground.
            > >
            > > The VHF is most likely looking for 4800 baud in NMEA format.
            > >
            > > Since u didn't specify I can only ass-u-me that u are not
            > connecting
            > > the ground to the NMEA-.
            > >
            > >
            > >
            > > --- In GarminGPSMAP60C_60CS@yahoogroups.com, Gary Turner
            > > <g.turner@> wrote:
            > > >
            > > > I'm only guessing/thinking - but I would have thought that NMEA
            > > would be constant transmit-only, but that the default garmin
            > protocol
            > > could be question/response.
            > > >
            > > > Was the GPS in NMEA mode, or Garmin mode?
            > > >
            > > > Being 2-wire only, the comms must use software handshake. I guess
            > > your radio must be able to simply suck up all the data. There
            > would be
            > > no way otherwise to send any XON/XOFF's.
            > > >
            > > > ----- Original Message -----
            > > > From: frans.plugge
            > > > To: GarminGPSMAP60C_60CS@yahoogroups.com
            > > > Sent: Friday, September 28, 2007 7:55 PM
            > > > Subject: [GarminGPSMAP60C_60CS] Serial Communication
            > > >
            > > >
            > > > Hi,
            > > >
            > > > When I connect my GPSMAP 60CS via the serial connection to my
            > PC with
            > > > only the Tx-line connected to the Rx of the PC, there is no
            > > > communication. Only when I also connected the Rx of the GPS to
            > the Tx
            > > > of the PC does the communication start. I'm trying to connect
            > the GPS
            > > > to a device (VHF radio with DSC), which only receives NMEA-
            > data and
            > > > therefore only has a Rx line.
            > > > Is anyone familiar with this problem (I'm using firmware 4.0)?
            > > >
            > > > Kind regards,
            > > > Frans
            > > >
            > >
            >
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