How to Connect a 9-Pin Serial Cable to a MAX232

Written by peter syslo
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How to Connect a 9-Pin Serial Cable to a MAX232
An example of the female end of a 9-pin serial cable (serial adaptor image by Paul Moore from Fotolia.com)

A MAX232 is an integrated circuit enabling serial communication between a computer and external electronic devices. The term "serial" means data is transferred and received one "piece" at a time, in a linear fashion. Interfacing a 9-pin serial cable, often called DB-9, to a MAX232 is a process of making three important connections. There must be a transmit, a receive and a ground connection between the DB-9 and the MAX232. The only other requirement is the connection of five capacitors to various pins of the MAX232. Once these connections are made, the completed serial interface is ready for computer configuration.

Skill level:
Moderate

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Things you need

  • MAX232 data sheet
  • Electronics breadboard
  • 7 jumper wires
  • MAX232 integrated circuit
  • 5 electrolytic capacitors (1 uF)
  • Five-volt DC power supply
  • Pinout for DB-9 connector
  • DB-9 connector (female)

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Instructions

  1. 1

    Locate the "GND" pin on the MAX232 using the data sheet. Insert the MAX232 into the breadboard and connect a jumper wire from the "GND" pin to circuit ground.

  2. 2

    Connect the positive side of the first capacitor to the "V+" pin of the MAX232. Connect the negative side -- which should have a white stripe -- of the capacitor to the "Vcc" pin of the MAX232.

  3. 3

    Connect the positive side of the second capacitor to the "Vcc" pin of the MAX232 and connect the negative side of the capacitor to circuit ground.

  4. 4

    Connect a jumper from the five-volt power supply to the "Vcc" pin of the MAX232.

  5. 5

    Connect the negative side of the third capacitor to the "V-" pin of the MAX232. Connect the positive side of the capacitor to circuit ground.

  6. 6

    Connect the positive side of the fourth capacitor to the "C1+" pin of the MAX232. Connect the negative side of the capacitor to the "C1-" pin of the MAX232.

  7. 7

    Connect the positive side of the fifth capacitor to the "C2+" pin of the MAX232 and connect the negative side of the capacitor to the "C2-" pin of the MAX232.

  1. 1

    Locate the "ground" pin on the DB-9 connector using the pinout. Insert the DB-9 into the breadboard and connect a jumper from the ground pin to circuit ground.

  2. 2

    Connect the "Received Data" pin of the DB-9 to the "T1OUT" pin of the MAX232 with a jumper.

  3. 3

    Connect the "Transmitted Data" pin to the "R1IN" pin of the MAX232 with a jumper.

  4. 4

    Connect a jumper from the "T1IN" pin of the MAX232 and leave the other end of the jumper free. This will be the transmit, or "TX," line.

  5. 5

    Connect a jumper from the "R1OUT" pin of the MAX232 and leave the other end free. This will be the receive, or "RX," line.

  6. 6

    Connect the "TX" and "RX" lines to a microcontroller or other device. After computer configuration, the serial connection is ready to use.

Tips and warnings

  • Make sure that the DB-9 pinout is for the "female" type of connector. The female end of a male-to-female DB-9 cable can be used instead of a female DB-9 connector. This tutorial is meant for the electrical connections only. Computer configuration is required for a working serial connection. It is a good idea to perform a computer backup or set a recovery point before connecting or configuring any new hardware.
  • Be aware of the polarity of the electrolytic capacitors. The negative side is the one marked with a stripe, usually white. These capacitors can explode if they are improperly connected. Perform all circuit connections before the serial cable is interfaced with the computer.

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