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&Sn
Data Set Ready Control
n = 0, 1, or 2
Default: &S1
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; allow it to act
normally; or set it to stay high until the modem disconnects, go low momentarily, and then
go high again.
&S0 forces DSR high.
&S1 allows DSR to act normally, that is, to follow CD.
&S2 sets up DSR so that it drops for one second on disconnect and then comes up again.
(If you want to set the drop time to something other than one second, change register S24.)
&RFn
CTS/RTS Interaction Control
n = 0 or 1
Default: &RF1
In normal operation, Clear to Send (CTS) follows Request to Send (RTS) when the modem
is online. In other words, if RTS goes off, CTS goes off. In some applications, however, it is
necessary for CTS to operate independently of RTS.
&RF0 enables CTS to follow RTS.
&RF1 enables CTS to operate independently of the state of RTS. See the &R command for
control of CTS.
&SFn
DSR/CD Interaction Control
n = 0 or 1
Default: &SF0
Normally, the Data Set Ready (DSR) signal follows the Carrier Detect (CD) signal. In other
words, if CD goes high, DSR goes high. In some applications, however, it may be
necessary for DSR to operate independently of CD.
&SF0 enables DSR to follow CD.
&SF1 enables DSR to operate independently of CD. For control of DSR, see the &S
command.
Chapter 3 - AT Commands
42
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