IBM Aptiva Handbook page 174

Table 14: Common modem commands
Code/Command Function
Hn Instructs the modem to go on-hook to disconnect a call or off-hook to make the phone line busy:
n=0 On-hook
n=1 Off-hook
In Requests specific product information on the modem:
n=0 Returns the default speed and controller firmware version (same as I3).
n=1 Calculates a ROM checksum and displays it on the DTE.
n=2 Performs a ROM check and calculates and verifies the checksum. Displays OK or ERROR.
n=3 Returns the default speed and controller firmware version (same as I0).
n=4 Returns the firmware version for the data pump.
n=9 Returns the country code.
Ln Sets the volume of the speaker on the modem:
n=0 Low volume
n=1 Low volume
n=2 Medium volume
n=3 High volume
Mn Controls when the modem speaker is in use:
n=0 Speaker is off.
n=1 Speaker is on except when receiving.
n=2 Speaker is on.
n=3 Speaker is off when dialing or receiving.
Nn Controls whether the local modem performs a modulation handshake with the remote modem at connection time to
negotiate between differing communication speeds:
n=0 Performs the handshake at the communication standard indicated in the ATB modem command and the S37
S register.
n=1 Starts the handshake at the communication standard indicated in the ATB modem command and the S37 S register
and then permits fallback to a lower speed during the handshake.
158 Appendix C: Modem information