M7 I/O Connections

The M7′s I/O Connector

On the front of the M7 series of transponders, is an Input / output (I/O) connector used to configure the unit.  This I/O connector supports RS232 serial data (422 optionally), as well as digital input and output.

The RS232 9-pin serial I/O connector is a female 9-pin D-subminiature connector having the following pins configuration. It is pinned out so that it may be plugged directly into a computer or PC’s 9-pin COM port.

db9

DB9 Female I/O connector

Front-view of DB-9 connector on modem (female)

Pin

Name

Dir

Function

Level / Specification

1

CD

out

Carrier detect

If enabled, indicates presence of carrier. Logical 0 (+ voltage on RS-232) means carrier is present. If disabled, it is asserted (0) whenever the modem is operational, and not in the configuration mode. It will be a 1 when the modem is in the configuration mode.

2

RxD

out

Receive data

Data out of the modem.

3

TxD

in

Transmit data
or
IN2

Data into the modem.

Also used as digital input IN2 for exception reporting. GND or floating for a 0, >3V for digital 1. If enabled for digital inputs, the serial data entering this pin is ignored (except in the command mode). Use the TRIGBITS command to set which bits are used as inputs.

4

DTR

in

Data terminal ready
or
IN0

Normally ignored by the RV-M7 modem. May control the power-state of the modem in low-power mode if this feature is enabled.

Also used as digital input IN0 for exception reporting. GND or floating for a 0, >3V for digital 1. Use the TRIGBITS command to set which bits are used as inputs.

5

GND

Ground connection

Signal and power ground

6

DSR

out

Data Set Ready

Normally is set to 0 when modem is powered on and running. Modem sets to a 1 when in low-power mode.

7

RTS

in

Request to send
or
IN1

Used to stop/start the flow of data coming out of the modem TxD pin. 0 = OK to send, 1 = don’t send. Leave disconnected if not used.

Also used as digital input IN1 for exception reporting. GND or floating for a 0, >3V for digital 1. Use the TRIGBITS command to set which bits are used as inputs.

8

CTS

out

Clear to send

Used to stop the flow of data going into the RxD pin from the device connected to the RV-M7. 0 = OK to send, 1 = don’t send. If the RV-M7 cannot accept more data, it will negate this signal (set to a 1).

9

Power

In/out

DC power (not ring signal)

User may supply the DC power to the modem on this pin.

Note: RS-232 signals use positive and negative voltages to represent digital 1s and 0s. A positive voltage is a 0, and a negative voltage is a digital 1.

This I/O pin-out allows the M7 to be directly plugged into a PC computer’s 9-pin serial port using a conventional 9-pin RS-232 serial cable. To connect it to a modem, or peripheral that has a serial port, you will need a “null-modem” cable.

Null Modem Cables

Sometimes, a “Null Modem” cable may be required to connect the M7 modem to another device. The specific connections are very dependent upon the type of hardware and handshaking used, but the following sections should help in configuring a null-modem cable.

How to use the handshaking lines in a null modem configuration? The simplest way is to don’t use them at all. In that situation, only the data lines and signal ground are cross connected in the null modem communication cable. All other pins have no connection. An example of such a null modem cable without handshaking can be seen in the figure below.

nullmodem

Simple Null-Modem Wiring Diagram

(Same wiring for male-to-male or female-to-femal cable)

Connector 1

Connector 2

Function

2

3

Rx

Tx

3

2

Tx

Rx

5

5

Signal ground

If you are connecting your M7 to a Lowrance or Garmin GPS display, then you will need a null-modem cable to connect the M7 to the display. Lowrance provides a serial cable for its GPSs with “pigtail” wires, so you can solder your own DB9 male connector to it, and plug the Lowrance directly into the M7.

To connect a Garmin GPS, use a null-modem cable to connect it to the M7, or the supplied Garmin serial cable and a “Null Modem Adaptor”.

Digital Inputs

The M7 GX Transponder has 3 digital inputs, called Trigger Bits. Trigger Bits are digital inputs that trigger the M7 GX to report its position and status. Normally these inputs are used for RS-232 signals, but they may be used for general-purpose digital inputs. The M7 GX may be configured to trigger a position/status report based upon the digital input bits state.

Important: If the digital input function is not needed, the TRIGBITS setting must be set to 0. This is the factory-default setting, and unexpected transmission may happen if the digital inputs are enabled and not used.

The status of all digital inputs is transmitted every time the unit reports its position.  This is not dependent upon how the TRIGBITS paramter is set. Each transmission, all digital input status is sent.

Starting with firmware version C2 and higher, the digital inputs have “memory” if they are enabled with the TRIGBITS command.  If you enable a bit or bits with the TRIGBITS command so that it triggers high, then the M7 will remember that a bit goes high if it does so, even momentarily.  For example, if a TRIGBIT bit goes high and then quickly goes back low, the M7 will remember this, and the next time it reports its position, will report the bit as “High”, even if it is low. Subsequent position transmissions will report it low, until it goes high again. If a bit is not configured as a TRIGBIT, then the M7 will report the state of the bit at the moment the GPS position is transmitted.

If you are not using digital inputs to initiate a transmission, the TRIGBITS should be set to 0. (TRIGBITS 0 command)

If the RV-M7 GX was configured to transmit less-often when it is not moving, activation of the digital inputs will override this causing the unit to report at the interval programmed with the TXRATE command. The digital inputs may be configured to be active high, active low, or active on a change in state. The following table lists the available digital inputs on the standard RV-M7 GX:

RS-232 Pin

Function

4 – DTR

Input 0

7 – RTS

Input 1

3 – TXD

Input 2

5 – Ground

GND

There are 3 commands that must be configured to use the digital inputs:

TRIGBITS x This command enables or disables individual bits for use as input triggers.

TRIGPOL x Sets the polarity of the input. 0=active high, 1=inverted, active low.

TRIGEX x Sets which bits are used to report on exception. Exception reporting is when a position/status report is generated when an input changes either low-to-high or high-to-low.

The xx parameter is the hex binary representation of the bits. Refer to the following table to see the value for x.

IN 2
(TXD)

IN 1
(RTS)

IN 0
(DTR)

Hexadecimal Representation

0

0

0

0

0

0

1

1

0

1

0

2

0

1

1

3

1

0

0

4

1

0

1

5

1

1

0

6

1

1

1

7

For example, to enable bits 0 and 2 (DTR and TxD pins) to be used as digital input, issue the following commend:

TRIGBITS 5

If the bits are to be normally active high, then the polarity must be set to 0 (TRIGPOL 0 command). To set bit 0 so that it is inverted (active low), use the following command:

TRIGPOL 1

This will cause the unit to transmit when bit 0 (DTR pin) is low.

To enable exception reporting, that is transmit when a pin changes from low-to-high or high-to-low, use the TRIGEX command. When TRIGEX is 0, all inputs are active either high or low. When a bit is set to 1 in TRIGEX, then that bit will cause the unit to transmit position/status anytime it changes state.

For example, to configure the unit to transmit position when bit 0 changes state, issue these commands:

TRIGBITS 1 (enables bit 0)

TRIGEX 1 (configures bit 0 for exception reporting)

To configure all bits to be used to report when they change, issue these commands:

TRIGBITS 7 (enables bit 0, 1 and 2)

TRIGEX 7 (configures bit 0, 1, and 2 for exception reporting)

To configure bit 0 to be used to report when it changes, bit 1 to cause a report when it goes low, and disable bit 2, use these commands.

TRIGBITS 3 (enables bit 0 and 1, disable 2)

TRIGEX 1 (configures bit 0 for exception reporting)

TRIGPOL 2 (configures bit 1 for active-low reporting)