Comtech EF Data SNM-1001 - Manual (Page 61)

Remote Control Operation SNM-1001 Network Control Modem
A–2 Rev. 1
A.1 General
Remote controls and status information are transferred via an EIA485 (optional EIA232C)
serial communications link.
Commands and data are transferred on the remote control communications link as
US ASCII-encoded character strings.
The remote communications link is operated in a half-duplex mode.
Communications on the remote link are initiated by a remote controller or terminal. The
modem never transmits data on the link unless it is commanded to do so.
Since the SNM-1001 operates in both Burst and Continuous modes, command and
command parameter selection will be dependent upon whether the Transmit Mode has
been configured as Burst or Continuous, and whether the Receive Mode has been
configured as Burst or Continuous. The SNM-1001 modem will default to Transmit
Burst, Receive Burst modes after a cold startup, or when a hard reset has been initiated.