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Troubleshooting: Using a Butt Set & Serial Communication

Previous Page: Section 5: How to Test 202, FSK, and RS-422/RS-485 Connections with a Butt Set
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How to Identify 202, FSK and RS-422/485 Pinouts with a Butt Set

What is a Butt Set?

A Phone Butt Set is a tool used by linemen to test telephone lines. Similar to a handset on a residential telephone, the Butt Set features an outgoing mouthpiece and an incoming receiver piece for two way communication. Most Buttsets all so feature a 12 button keypad and a few various other features.

The purpose of the Butt Set is to allow telephone Lineman handset to tap into a phone line to ensure it is working properly. To do this, the Butt Set will also have two cables, typically alligator clips, to attach to the line's tx and Rx ports. When connected properly, the Butt Set is essentially indistinguishable from regular subscriber equipment.

While it may have an odd, even silly name, the Butt Set is a critical piece of testing equipment for linemen. Other common names are Test Set and Lineman's Set. Older telephone linemen also referred to the Butt Set as a "Goat". The name effectively comes from the act of butting in on a live line.

Why Would you Need to Identify Pinouts with a Butt Set?

If you are using a telephone butt tester to identify pinouts, you are most likely trying to connect to legacy gear. The most common application for identifying pinouts is to verify connectivity between a remote site or residence, and the central office's main or intermediate distribution frames.

If you're working with a 202, FSK or RS-422/485 connection, you can use a butt set to identify transmit (tx) pins and receive (rx) pins.

  1. Connect your butt set to the pin you want to identify.
  2. If it's a transmit pin, you'll hear a series of tones in the earpiece.
  3. For more information on testing ports with a butt set, see Section 5, "How to Test RS-422 and RS-485 Connections with a Butt Set."

The Telephone Butt Set is an integral piece of data communications equipment. It is a special tool used by technicians for installing and testing local loop telephone lines. With the tool, you can verify connectivity through common modes of communication, such as 202 Modems, FSK, RS-422, and RS-485.

How to Identify Serial Device Pinouts with a PC

If you're having problems connecting to a serial device, you can use a PC HyperTerminal connection to identify its pinouts. The most common PC COM port is going to be a RS 232 or a DB9 connection. In fact, all DPS devices use common USB to Serial RS 232 ports and DB9 ports.

  1. Connect the COM port of your PC to the serial port of the device using a straight-through serial cable and try establishing a HyperTerminal connection (may require a USB to Serial cable).
  2. If you can connect via HyperTerminal, you know the device can connect to a standard PC COM port.
Standard PC COM port pinout
Wiring diagram of a 9 pin serial cable straight-through pinout
  1. Since all PC COM serial connectors have the same standard pinout, you have a reference for identifying the pinout of the serial device's pinout (See Figure 1 for a standard COM port pinout). Make sure that the cable is properly connected. Loose cables can cause device communication issues.
    Note: Your connection problems may also be caused by an incorrect baud rate. If you can successfully connect via HyperTerminal, check your PC's baud rate and apply it to all equipment that connects to this device.
    Note: Your serial device may require handshaking signals. If you can successfully connect via Hyperterminal, check to make sure that all equipment that connects to your serial device supports handshaking.
  2. If you can't connect via HyperTerminal, it may be an indication that the serial device's port or the cable you're using may be broken.

For Windows 10 devices that lack the DB9 connector, you may consider purchasing an adapter. If your computer has this connector, then you will want to roll back the driver version. This is because Windows 10 included a driver update that may cause some cables to not function properly. For desktop computers, you may also purchase a DB9 PCI expansion card, which is also useful for having additional serial ports on your workstation.

Next Page: Section 8: Serial Remotes Can't Connect to Master
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