Globalstar Product Management – Technical Support

Extended Length Cables for RS232 and TTL Data

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With the exception of the new GSP-1700 handheld phone, all Globalstar products use serial RS232 for data communication and use serial TTL for diagnostic software communications. In a number of instances, customers simply insert extra serial cables between their computer and the satellite phone/modem and then find that the computer is no longer able to communicate properly.  This is because of cross-talk in the serial cables and the fact that serial cables are designed for a maximum length of 20 feet (all cables connected together).  This is usually far too short for many connections to satellite modems.  Following is a very easy solution to this problem.

For customers who need to extend their data cables beyond the length of the standard cables, we have found that, in most situations, CAT5 cable can carry RS232 serial data signals or TTL signals up to 400 feet. An easy way of creating an extended length serial cable is to use CAT5 cabling with standard RJ45 connectors and appropriate RJ45-DB9 adapters. This allows the installer to use readily available COTS (commercial off-the-shelf) Ethernet cable products and standardized CAT5 installation procedures. The procurement and installation costs are usually far lower with this approach than with using custom cables and custom signal drivers.

The instructions are fairly simple:

1. Purchase two DB9-RJ45 adapters from Radio Shack or another electronics store. You should obtain one RJ45-to-DB9-Male adapter, and one RJ45-to-DB9-Female adapter. If the electronics store has only one gender available, then purchase a gender changer so that you end up with a male and female DB9

2. Since there are only 8 pins on the RJ45 and 9 pins on the DB9, you cannot carry all nine of the DB9 pins from end-to-end. We have designed two types of DB9-to-RJ45 wiring, depending on the type of Globalstar phone you are using. These wiring plans are included in the attached document. Wire both of the RJ45 adapters in exactly the same way, so that there will be a straight-through connection. In other words, pin 1 of the DB9M should use the same RJ45 wire as pin 1 of the DB9F, so that when you connect a standard RJ45-terminated Ethernet cable between the two adapters, pin 1 will be connected to pin 1. Do likewise for the rest of the pins.

3. Connect a standard RJ45-terminated CAT5 cable between the adapters

We have found that, depending on CAT5 cable quality, we can easily extend serial connections 400 feet using this method. We have never had a problem with CAT5 quality, but we recommend that you ALWAYS check the adapters and the cable as an assembly before installing the CAT5 cable.

It is possible that there will be problems with data cable installations which traverse electrically noisy environments. Most often, this is due to unwanted voltage/currents in the data cable, caused by the environment. Additional reasons could be excessive crosstalk within the cable and, sometimes, excessive signal attenuation.

Excessive near-end crosstalk is a function of the design and manufacture of the cable. Excessive crosstalk can cause: * High error rates * An inoperative network or attached device * In extreme cases, false readings from the diagnostic procedures

We have found that we can often solve the problems with these serial connections by simply using a CAT5 cable with a shield and grounding the shield of the cable at one end. Once we ground it, flaky and/or nonworking cables often start to work just fine. This is a convenient solution when working with cables that are already installed in tight places such as boats.

DB9 to RJ45 Adapter

Type 1 – Use this wiring plan for GSP-1620 Data Port

The GSP-1620 modem provides a DSR signal, which some computers use to determine if a modem is ready to receive commands.Since there are only eight wires available an an RJ45 connector, and since RI (Ring Indicator signal) is not used very much by data communication devices, the following wiring plan is designed to provide DSR connectivity, but does not carry the RI signal to the DB9 connector.

DB9 Sequence

Type 1

w/DSR

DB9 Connector RJ45Connector
DCD 1 2
RD 2 5
TD 3 6
DTR 4 3
GND 5 4
DSR 6 1
RTS 7 8
CTS 8 7
RI 9

RJ45 Sequence

Type 1

w/DSR

DB9 Connector RJ45Connector
RI 9 Not used
DSR 6 1
DCD 1 2
DTR 4 3
GND 5 4
RD 2 5
TD 3 6
CTS 8 7
RTS 7 8


Type 2 – Use this wiring plan for GSP-1600, GSP-2900, GCK-1410 Data Communications cables and for ALL TTL cables

The above Globalstar products do not supply a DSR signal on their data ports. Therefore, it is essential that DSR not be connected because the “floating” voltage in the wire will cause the computer’s serial port to behave improperly.

In the case of a TTL diagnostic communications extension cable, pin 6 is unused for diagnostic communications and, for various additional reasons, it is important that this pin not be carried through the extended length cable. Standard length Globalstar diagnostic communications cables supply power to the Globalstar device through the standard length cable. However, when using extended length cables, the end-to-end voltage drop would be too great if the power was applied in the same way. Therefore, it is essential that the diagnostic communications cable is NOT connected to a power supply when an extended length cable is used. Instead, power the Globalstar device locally and only use the extended length TTL cable to carry the TTL communications to the monitoring/controlling computer.

Contact Globalstar Customer Care if you have ANY questions about the use of extended length data cables for diagnostic communications.

DB9 Sequence

Type 2

w/RI

DB9 Connector RJ 45Connector
DCD 1 2
RD 2 5
TD 3 6
DTR 4 3
GND 5 4
DSR 6
RTS 7 8
CTS 8 7
RI 9 1

RJ45 Sequence

Type 2

w/RI

DB9 Connector RJ 45Connector
DSR 6 Not used
RI 9 1
DCD 1 2
DTR 4 3
GND 5 4
RD 2 5
TD 3 6
CTS 8 7
RTS 7 8

 

Additional keywords:  long data cables ethernet connector

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Written by Joseph Crowley

June 16, 2008 at 9:10 am

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