User manual

76 MultiModemISI Hybrid Series, ISIHI-2S
Chapter 4—MODEM AT Commands, S-Registers, Result Codes
Modem
RS-232 Interface Commands
These commands define how an ISIHI-2S modem uses and responds to standard RS-
232 signals.
&C
n Carrier Detect Control
n = 0 or 1
Default: &C1
The &C command lets you control the Carrier Detect (CD) signal on the RS-232/V.24
interface. This is a signal from the modem to your computer indicating that the carrier
signal is being received from a remote modem. Normally, CD goes
high (turns on) when
the modem detects a carrier on the communications link and drops (turns off) when it
loses the carrier. By using &C, 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.)
&C0 ignores the state of the carrier from the remote modem. CD is forced high.
&C1 allows CD to act normally—to go high when the modem detects a carrier, and to
drop when it loses the carrier.
&D
n 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 the DTR signal and treat it as always on.
&D1 causes the modem, if in online data mode, to enter command mode, issue an OK
and remain connected when the DTR drops.
&D2 causes the modem to hang up when DTR drops while the modem is in online data
mode.
&D3 causes the modem to reset when DTR drops . It will also hang up if it is online.
&S
n Data Set Ready Control
n = 0 or 1
Default: &S0
Use the &S command to control the state of the Data Set Ready (DSR) signal on the RS-
232/V.24 interface. Normally, DSR follows CD. You can force the signal high or allow it to
act normally.
&S0 forces DSR high (on).
&S1 allows DSR to act normally, that is, to follow CD.