Black Box MD1641A, MD1640A Async/Sync Mode Switching &M, Synchronous Transmit Clock Select &X

User Guide for Series II Modems

The #V command gives the user the option of including V.32terbo as part of the handshaking process in both Orignate and Answer modes. Entering AT#V0&W0<CR> includes the V.32terbo mode in handshaking. Entering AT#V1&W0<CR> disables the Series II Modem 336 from using V.32terbo mode in the handshaking process (default).

Async/Sync Mode Switching &M

This command can be used to set the on-line mode to either synchronous or asynchronous. AT&M0 will set the Series II Modem to Asynchronous mode, and all communications will be asynchronous in both On-line and Command modes. AT&M1 causes the Modem to com- municate asynchronously when in Command mode and switch to syn- chronous mode while on-line. The modem defaults to &M0 (asynchronous communications) on reset or power-up.

Synchronous Transmit Clock Select &X

The &X command selects the Synchronous Transmit Clock Source in conjunction with DIP-Switch #11. DIP-Switch #11 in the UP position enables External clocking. DIP-Switch #11 in the DOWN position enables Internal clocking (default position). External clocking is when the DTE provides transmit clocking to the modem on pin 24 of the RS232C interface.

&X0 is the default setting, which allows DIP-Switch #11 to control Internal/External Clocking (default Internal). Internal clocking is when the modem provides transmit clock to the DTE on pin 15 of the RS-232C/V.24 interface. The &X1 command overrides DIP-Switch #11 and selects External clocking. If DIP-Switch #11 is UP (External clocking), you can not override Internal clocking. &X2 enables Slave Clocking. The &X2 Command causes the Series II Modem to generate the transmit clock timing (pin 15) from the receive clock (pin 17) from the DTE (therefore 15 and 17 are the same). In this mode (Slave Clocking), all timing is controlled by the receive clock.

62