Comtrol AT Command Set Rev A - Manual (Page 129)

AT Commands Reference Manual
100722B Conexant 3-103
S19 - Reserved
S19 is supported for backwards compatibility only. No value can be written. Responds
with default value.
Range: None
Default: 0
S20 - Reserved
S20 is supported for backwards compatibility only. No value can be written. Responds
with default value.
Range: None
Default: 0
S21 - V.24/General Bit Mapped Options Status
S21 indicates the status of command options.
Default: 52 (34h) (00110100b)
Bits 0 - 1 Reserved (0)
Bit 2 CTS behavior (&Rn)
0 = CTS tracks RTS (&R0)
1 = CTS always on (&R1) (Default.)
Bits 3-4 DTR behavior (&Dn)
0 = &D0 selected
1 = &D1 selected
2 = &D2 selected (Default.)
3 = &D3 selected
Bit 5 RLSD (DCD) behavior (&Cn)
0 = &C0 selected
1 = &C1 selected (Default.)
Bit 6 DSR behavior (&Sn)
0 = &S0 selected (Default.)
1 = &S1 selected
Bit 7 Long space disconnect (Yn)
0 = Y0 (Default.)
1 = Y1