TECHNICAL BULLETIN #122 - Rev 1.10 (8/30/96) ============================================================================== TITLE : Testing an RS-232 Connection (Paper-Clip Test) PRODUCT : Procomm Plus 4.x, 3.x ============================================================================== No characters appearing on the Terminal screen? Suspect your serial port or cable? Here's how to test the send data and receive data lines of your serial port and RS-232 cable. COMMON SERIAL PORT PROBLEMS Several things can prevent characters from appearing on your screen when you type to your modem or to another computer. Check these first before testing your port. * Resolve any port conflicts. Each serial device on your computer must have a unique base port address (BPA) and interrupt request line (IRQ) assigned to it. For help in resolving IRQ and BPA conflicts, see technical bulletins #89 (PROCOMM PLUS for Windows) and #90 (PROCOMM PLUS for DOS). * Make sure you are using the proper cable for your type of connection. A PC-to-PC connection requires a "null-modem" cable (see technical bulletin #87), whereas a PC-to-modem connection requires a standard serial cable with all lines connected straight through. * If connecting two PCs, be sure line settings in the communications programs are identical on both machines (e.g., no parity, 8 data bits, 1 stop bit). * If connected to a modem, make sure echo is turned on and quiet mode is turned off in the modem. Type ATE1Q0 from your terminal screen, then type AT key. You should see the "AT" appear on your screen, followed by an "OK" response from your modem. * In a PC-to-PC connection with Procomm Plus set to FULL DUPLEX, you will not see what you type on your terminal screen, but the characters should appear on the screen of the computer you are connected to. RS-232 PORT DESCRIPTION A serial port has either 9 or 25 pins. To locate your serial port, look on the back of your computer for "male" pins in a "D" shell. These two figures will give you a better idea about the physical appearance of those ports. --------------- \ 1 2 3 4 5 / \ 6 7 8 9 / \---------/ 9 - pin RS232 port ----------------------------------------- \ 1 2 3 4 5 6 7 8 9 10 11 12 13 / \ 14 15 16 17 18 19 20 21 22 23 24 25 / \-----------------------------------/ 25 - pin RS232 port Pin 2 is used to send the data to, and pin 3 to receive data from, another serial device. By connecting those two you can make a closed circuit that will echo characters you type back to your Procomm Plus terminal screen. Pin 4 carries the RTS (ready to send) signal and Pin 5 the CTS (clear to send) signal. RTS and CTS lines are used for Hardware Flow Control and are discussed below. PAPER-CLIP TEST Due to low voltages, there is no risk of electric shock when connecting two pins on the RS232 port. 1. You will need a metal paper clip (without plastic coating) or a screwdriver to establish a circuit between pin 2 and pin 3 2. Have your computer running Procomm Plus 3. Turn Hardware Flow Control OFF for the duration of this test: * Procomm Plus 4.x Setup | Data Modem/Connection | Connection Setup | Use hardware flow control * PROCOMM PLUS for Windows 3.x Setup | Data | Data Connection | General | Use hardware flow control * PROCOMM PLUS (DOS) Setup | Terminal Options | D - Hard flow control (RTS/CTS) 4. Set Procomm Plus to FULL DUPLEX mode: * PROCOMM PLUS for Windows 4.x Setup | Data | Data Options | Advanced | Duplex * PROCOMM PLUS for Windows 3.x Setup | Data | Port Settings | Full Duplex * PROCOMM PLUS (DOS) Setup | Terminal Options | B - Duplex 5. Disconnect the serial RS-232 cable from the back of your computer. 6. Connect ONLY pins 2 and 3 with the metal object. (Press it against them and hold it there). 7. Press an alphabetic key on your keyboard and see if it shows up on your terminal screen. If the letter shows up, connect the cable back to the computer and test the far end of the cable (the one that plugs into the other serial device -- an RS-232 serial port or a modem) and repeat steps 6 and 7. Serial cables have "female" connectors, so you will find holes instead of pins. A paper clip should fit firmly into openings 2 and 3. The positions of those openings will be reversed from the ones on the "male" side, however. The following two diagrams illustrates the locations of the send and receive lines (pin slots 2 and 3) in a serial cable. --------------- \ 5 4 3 2 1 / \ 9 8 7 6 / \---------/ 9 - pin female RS232 serial cable ----------------------------------------- \ 13 12 11 10 9 8 7 6 5 4 3 2 1 / \ 25 24 23 22 21 20 19 18 17 16 15 14 / \-----------------------------------/ 25 - pin female RS232 serial cable HARDWARE FLOW CONTROL LINES MUST BE PRESENT IN CABLE If the test indicates characters are being sent and received from the port and/or cable properly, the cause of the problem is not in the hardware component that was tested. But only the SD and RD (send data and receive data) lines are tested; there could still be problems with other lines in the cable. The RTS/CTS lines, which carry flow control signals, are primary suspects. Hardware (RTS/CTS) flow control signals are carried by pins 4 and 5 in your serial port and cable. If these lines are missing in your cable (a common problem), Procomm Plus may attempt to send characters correctly, will sense that it does not have permission to send, and will wait for the CTS signal to be asserted. Those two lines are used in PC-to-modem communications and if missing or defective, will prevent you from sending characters to your modem normally. ============================================================================== To ensure that you have the latest version of this document, compare its revision number to that of the same document on any of our support sites. This technical bulletin may be copied and distributed freely as long as it is distributed in its entirety and it is not distributed for profit. Copyright (c) 1996 Quarterdeck All rights reserved. ==============================================================================