Interface Commands - Multitech MultiModem MT2834MR6 User Manual

3.9 RS-232 Interface Commands
These commands define how am MT2834MR6 modem will use and respond to standard RS-232 signals.
&Cn Carrier Detect Control
n = 0, 1, 2, or 4
Default: &C1
The &C command lets you control the Carrier Detect (CD) signal on the RS-232/V.24
interface. Normally, CD goes high when the modem detects a carrier on the
communications link, and drops when it loses the carrier. By using &C, however, you can
force the signal to stay high, or to drop momentarily when the remote modem disconnects.
(This option is useful with some CBX phone systems and mainframe front ends, which
require CD to act in this manner). You can also force the modem to reset when the CD
signal drops.
&C0 forces CD high.
&C1 allows CD to act normally—to go high when the modem detects a carrier, and to drop
when it loses the carrier.
&C2 causes CD to drop for one second on disconnect, and then go high again. (If you want
to set the drop time to something other than one second, change register S24).
&C4 resets the modem when CD drops.
&Dn Data Terminal Ready Control
n = 0, 1, 2, or 3
Default: &D2
The Data Terminal Ready (DTR) signal on pin 20 of the RS-232/V.24 interface must be
high, or "on," in order for the modem to operate. A high DTR signal tells the modem that the
computer it is connected to is ready to communicate through the modem.
The DTR signal can also be used to cause the modem to reset to its default parameters, as
if you had given the modem an ATZ command.
&D0 (or &D) causes the modem to ignore DTR.
&D1 causes the modem to hang up when DTR drops. While DTR is low, the modem
accepts commands, but will not dial or auto-answer until DTR goes high again.
&D2 acts the same as &D1.
&D3 causes the modem to reset when DTR drops . It will also hang up if it is online.
&Rn Clear to Send Control
n = 0, 1, or 2
Default: &R1
The &R command lets you control the state of the Clear to Send (CTS) signal on pin 5 of the
RS-232/V.24 interface. Normally, CTS follows RTS when the modem is online. You have
three choices. You can force the signal high, allow it to act normally, or set it to stay high
until the modem disconnects, go low momentarily, and then go high again. The last option
is useful with CBX phone systems and mainframe front ends that require CTS to act in this
manner.
&R0 lets CTS act normally, that is, to follow RTS.
&R1 forces CTS high. When the modem goes online, CTS still provides flow control.
&R2 lets CTS drop on disconnect for the time set by register S24, then go high again.
Chapter 3 - AT Commands
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