Section 7b: Identify 202, FSK and RS-422/485 Pinouts with a Butt Set

What is a Butt Set?
A Butt Set is a tool used by linemen to test phone 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 Butt Sets all so feature a 12 button keypad and a few various other features. The purpose of the Butt Set is to allow Linemen to tap onto a phone line to ensure it is working properly. To do this, the Butt Set will also have two cables, while some sort of alligator clip, to attach to the line. While it may have an odd, even silly, name, the Butt Set is a critical piece of testing equipment for linemen.

If you're working with a 202, FSK or RS-422/285 connection, you can use a butt set to identify transmit 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."

Why Would you Need to Identify Pinouts with a Butt Set?
If you are using a Butt Set to identify pinouts, you are most likely trying to connect to legacy gear.

Section 7c: 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.

  1. Connect the COM port of your PC to the serial device's port and try establishing a HyperTerminal connection.
  2. If you can connect via HyperTerminal, you know the device can connect to a standard PC COM port.
Standard PC COM port pinout
  1. Since all PC COM ports 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.)
  2. 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.
  3. 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.
  4. If you can't connect via HyperTerminal, the serial device's port may be broken.

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