132 MAN: HYDRA-II Modem Configuration Notes The following notes may be helpful in establishing your modem environment. Make sure that the carrier detect signal (pin 8 from the modem's RS-232C connector) is wired to pin 3 on HYDRA's red connector or pin 1 for units equipped with DE-9 connectors.  This allows HYDRA to detect when the modem has lost the carrier signal and perform cleanup functions on the port. Make absolutely sure that the callback port is not configured for DTR  flow control.  Generally, the attached modem will drop carrier detect and hang up the phone line when HYDRA toggles DTR (normally or abnormally).  Most modems will not respond to dialing commands if DTR from HYDRA is low.  We recommend that you stay away from DTR  flow control when using these devices types.    Make sure that all modems attached to HYDRA are set as follows: 1) Set the Modem's Carrier Detect to function normally (&C1) 2) Set modem's DTR recognition from HYDRA to hang up the telephone line and reset itself (&D3). Note: if your modem does not support this command use (&D2) 3) Suppress result messages such as CONNECT 2400 using (Q1) 4) Disable the modem from echoing data sent from HYDRA back to the same HYDRA port (E0) 5) Instruct the modem to answer the telephone line on the first ring (S0=1) Echo features of modems are to inform you of the success or failure of the dialing process when communicating with the modem.  HYDRA doesn't care and doesn't want to see them.  In fact, if HYDRA does see them, it usually results in a "ringing" situation.  When HYDRA sees an input character from the modem, it echoes the character back (thinking a terminal must have sent it).  The modem sees the echoed-back character and echoes it right back to HYDRA.  HYDRA and the modem will keep doing this to the character forever causing the entire HYDRA performance to degrade. High Speed Modems Additional considerations should be followed when using modems with baud rate capabilities greater than 2400 bps (V.32/V.42). 1) Set modem's serial port flow control to Xoff/Xon. Do not use Xoff/Xon "Transparancy" or "Pass-Through" mode. This will cause the buffering or pacing of data to become corrupted. 2) If the modem contains a serial port "Bps Rate Adjust" feature it should be disabled. You want the serial port of the modem to be locked at the highest speed  possible. For example a V.32/V.42 modem would normally run with a maximum serial baud rate of 19.2bps. Since modems of this type have independant DTE (modem serial port to HYDRA) and DCE (HYDRA modem to user's modem) baud rates, the HYDRA modem will use a buffering or pacing technique should the incoming caller connect at anything lower than 19.2bps. This is where Xoff/Xon flow control becomes critical. 3) The HYDRA port that this modem will connect to should be configured with a fixed baud rate of 19.2 using Xoff/Xon as the method of flow control. (See DSPLY BAUD and DSPLY TYP1  diagnostic commands for more details.) Testing the Callback Sequence If you are having problems with callback, you may want to verify that the callback sequence is correct for the type of modem attached to the port.  To verify the entire sequence, disconnect the modem from the port and connect a terminal directly to the HYDRA port.  The terminal must be configured with the same communication parameters as those used by the modem.  Invoke the normal HYDRA logon sequence to identify your terminal and when prompted for a password enter the password associated with the callback number in question.  The autodial command sequence, that HYDRA thinks it's sending to a modem, will be displayed on your terminal.  Use the display to verify the commands and sequence.  If no data is displayed, check the connection and configuration of the port.  Finally, check the DSPLY DIAL table to make sure it includes a "*M" which sends a carriage return (or [CTRL-M] ) to the modem. Most modems will not dial until a carriage return immediately follows the telephone number to be dialed.