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Modem AT Commands, S Registers and RS-232C pins

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| Modem AT Command | S Registers | RS-232C pin assignments |

AT Options / Details Chipset / Protocol
+++ Escape Code All
A/ Repeat Last Command All
A> Continuously Repeat Command USR
AT Command Mode Prefix All
AT#CID=n n=0 Disable caller ID
n=1 Enable caller ID in readable format
n=2 Enable caller ID in HEX format
Must have feature #142. Type ATi10
AT$ HELP, Command Summary USR
AT%Cn n=0 Data compression disable
n=1 MNP5 enable
n=2 V.42 enable
n=3 V.42bis and MNP5
V.34, Rockwell, Compression selection
AT%En n=0 Do not request retrain
n=1 Enable monitoring and retraining
if line is bad
n=2 Enable monitoring and retraining
if line is bad, wait one minute
before renogotiating higher speed
V.32 retraining
AT%Fn n=1 Select 75Tx/1200Rx
n=2 Select 100Tx/75Rx
n=3 Select V.23 half-duplex
Optional feature #121. Data echo options
AT%Gn n=0 Disable V.32bis rate negotiation
n=1 Enable V.32bis rate negotiation
V.32 Initiation of rate renegotiation
AT%L Report received signal level
009=-9 dBm (or more)
010=-10 dBm etc.
043=-43 dBm (or less)
Rockwell. Returns value representing signal level in -dBm. The smaller the number, the better the connection.
AT%Q Report line signal quality
Range of 0-128
Rockwell. Lower the number, better the line. Reading is instantanteous, repeat serveral times for acurate reading.
AT&$ HELP, Ampersand Commands USR
AT&An n=0 Disable /ARQ Result Codes
n=1 Enable /ARQ Result Codes
n=2 Enable /Modulation Codes
n=3 Enable /Extra Result Codes
Result codes-All
AT&Bn n=0 Floating DTE Speed
n=1 Fixed DTE Speed
n=2 DTE Speed Fixed When ARQ
DTE speed variables
AT&Cn n=0 DCD Always On
n=1 Modem Controls DCD
Data Carrier Detect
AT&Dn n=0 Ignore DTR
n=1 On-Line Command Mode
n=2 DTE Controls DTR
n=3 Reset modem (ATZ)
Select modem reaction to DTR. Works with &Q command
AT&Fn n=0 Load Factory 0, no FC
n=1 Load Factory 1, HW FC
n=2 Load Factory 2, SW FC
Load Factory Default
AT&Gn n=0 No Guard Tone
n=1 550 Hz Guard Tone
n=2 1800 Hz Guard Tone
Guard Tone
AT&Hn n=0 Disable TX Flow Control
n=1 CTS
n=2 Xon/Xoff
n=3 CTS and Xon/Xoff
USR, serial port flow control
AT&In n=0 Disable RX Flow Control
n=1 Xon/Xoff
n=2 Xon/Xoff Chars Filtered
n=3 HP Enq/Ack Host Mode
n=4 HP Enq/Ack Terminal Mode
n=5 Xon/Xoff for non-ARQ Mode
USR, serial port flow control
AT&Kn n=0 Disable Data Compression
n=1 Auto Data Compression
n=2 Enable Data Compression
n=3 Selective Data Compression
USR, data compression control
AT&Kn n=0 Disable flow control
n=3 Enable bi-directional hardware
(RTS/CTS) flow control
n=4 Enable software (XON/XOFF)
n=5 Enable trnasparent flow control
n=6 Enable both hardware and software
flow control
Rockwell, serial port flow control
AT&Mn n=0 Normal Mode
n=4 ARQ/Normal Mode
n=5 ARQ Mode
USR Asynchronous/Synchnous mode
AT&Nn n=0 Highest Link Speed
n=1 300 bps
n=2 1200 bps
n=3 2400 bps
n=4 4800 bps
n=5 7200 bps
n=6 9600 bps
n=7 12000 bps
n=8 14400 bps
n=9 16800 bps
n=10 19200 bps
n=11 21600 bps
n=12 24000 bps
n=13 26400 bps
n=14 28800 bps
n=15 31200 bps
n=16 33600 bps
AT&Pn n=0 N.American Pulse Dial
n=1 UK Pulse Dial
USR pulse dial selection
AT&Pn n=0 N.American Pulse Dial
(39%/61% and 10PPS)
n=1 UK/Hong Kong Pulse Dial
(33%/67% and 10PPS)
n=2 39%/61% and 20PPS
n=3 33%/67% and 20 PPS (Japan)
Rockwell make/break ratio for pulse dial
AT&Q n=1 Synch mode 1
n=2 Synch mode 2, dial stored number
when DTR makes transition
n=3 Synch mode 3, manual dialing
n=4 Reserved
n=5 Reliable Asynch mode
n=6 Normal Asynch mode
Rockwell asynch/synch mode
Same as &M, depending on &F
AT&Rn n=1 Ignore RTS
n=2 RX to DTE/RTS high
AT&Sn n=0 DSR Always On
n=1 Modem Controls DSR
AT&Tn n=0 End Test
n=1 Analog Loopback (ALB)
n=3 Digital Loopback (DLB)
n=4 Grant Remote DLB
n=5 Deny Remote DLB
n=6 Remote Digital Loopback
n=7 Remote DLB With Self Test
n=8 ALB With Self Test
AT&Un n=0 Variable link rate floor.
n=1 Minimum link rate 300 bps
n=2 Minimum link rate 1200 bps
n=3 Minimum link rate 2400 bps
n=4 Minimum link rate 4800 bps
n=5 Minimum link rate 7200 bps
n=6 Minimum link rate 9600 bps
n=7 Minimum link rate 12000 bps
n=8 Minimum link rate 14400 bps
n=9 Minimum link rate 16800 bps
n=10 Minimum link rate 19200 bps
n=11 Minimum link rate 21600 bps
n=12 Minimum link rate 24000 bps
n=13 Minimum link rate 26400 bps
n=14 Minimum link rate 28800 bps
n=15 Minimum link rate 31200 bps
n=16 Minimum link rate 33600 bps
AT&V Display configuration information Rockwell
AT&Wn n=0 Store Configuration 0
n=1 Store Configuration 1
AT&Yn n=0 Destructive
n=1 Destructive/Expedited
n=2 Nondest./Expedited
n=3 Nondest./Unexpedited
AT&Zn=s Store Phone Number All
AT&Zn? Query Phone Number


AT)Mn n=0 Adust transmit level if remote is set
to )M1, otherwise -10 dBm
n=1 Will try to adust power leve to less
than -10 dBm with MNP 10
Optional feature #144. Transmit level adjustment for cellular connection.
AT*B Display blacklisted numbers as defined by country requirements. optional feature #123. Used by countries that have permanently forbidden numbers.
AT*C Set configuration password Optional feature #124
AT*E Exit secure access remote configuration Optional feature #124
AT*Hn n=1 Negotiate at highest supported speed
n=2 Negotiate link at 1200bps
n=3 Negotiate link at 4800bps
Link Negotiation Rate
AT*L List callback security passwords Optional feature #124
AT*NC? Display country specific configurations Optional feature #120
AT*NCn n=ID of specific country Optional feature #120
AT*Pn:word: n=0-19 passwords and tel. numbers Optional feature #124
AT*R Activate remote configuration mode. Optional feature #124, works with *C
AT*R Request secure access mode Optional feature #124
AT+FAA=n n=2 Activate silent answer for class 2 fax
n=4 Activate silent answer plus for class
2 fax


AT+FAE=n n=1 Activate Adaptive Answer
n=3 Activate silent answer for class 1 fax


AT+MS Modulation control
V.34 only
AT+MS= n=0 Automode Disabled
n=1 Automode enable using V.8 or
V.32bis Annex A
V.34 only. Automode does not work with Bell 212
AT+MS= 28800,26400 etc. default for V.34 is 28800 V.34 only
300,1200,2400 etc. default for V.34 is 300bps V.34 only
AT+MS= n=0 V.21, 300bps
n=1 V.22, 1200bps
n=2 V.22bis, 1200/2400
n=3 V.23 bisynch 75/1200
n=9 V.32, 4800/9600
n=10 V.32bis, 4800/7200/9600/12000/
n=11 V.34, 2400/4800/7200/9600/
n=64 Bell 103, 300bps
n=69 Bell 212, 1200bps
n=74 V.FC, 14400/16800/
V.34 only
AT+MS? Reports MS options V.34 only
AT-B Forced fallback to 1200 Optional feature #143
AT-Cn n=0 MNP 10 enabled, sync mode
n=1 MNP 10 enabled, asynch mode
n=2 MNP 2 enabled
n=3 MNP 3 enabled
Optional feature #143
AT-Kn n=0 Do not convert LAPM to MNP
n=1 Convert LAPM connection to
MNP 10
n=3 Enable MNP 10 extended services
Optional feature #143
AT-Qn n=0 Enable fallback to V.22/V.22bis
n=1 Disable fallback
Optional feature #143
AT-Un n=0 Allow attenuation to -10 dBm
n=1 Allow attenuation to -18 dBm
n=2 Allow attenuation to -22 dBm
n=3 Allow attenuation to -25 dBm
n=4 Force 2400 bps transmit level to
-10 dBm
n=5 Force 2400 bps transmit level to
-18 dBm
n=6 Force 2400 bps transmit level to
-22 dBm
n=7 Force 2400 bps transmit level to
-25 dBm
Optional feature #143. Forced transmit level change during fall forward


Hayes - Answer Phone Line
ATBn n=0 V32/CCITT 1200b[s
n=1 Bell Standard 212A 1200bps
n=2 V.23 originate: T75/R1200 when
DTE speed is 1200 bit/second.
V.23 answer: T75/R1200 when
DTE speed is 1200 bit/second.
n=3 - V.23 originate: T1200/R75 when DTE speed is 1200bps.
V.23 answer: T1200/R75 when
DTE speed is 1200BPS.
n=6 V.26 bis when line speed is 1200bps
n=15 V.21 when line speed is 300bps
n=16 Industry Standard 103 when speed
is 300 bps.
n=30 V.22 bis when speed is 2400bps
n=32 V.26 bis when speed is 2400bps
n=41 V.32 when line speed is 4800bps
n=52 V.32 bis when speed is 7200bps
n=60 V.32 when speed is 9600bps
n=64 V.FC when speed is 9600bps
n=70 V.32 bis when handshake begins
at 12000 bps.
n=71 V.FC when handshake begins at 12000 bit/second.
n=75 - V.32 bis when handshake begins at 14400 bit/second.
n=76 - V.FC when handshake begins at 14400 bit/second.
n=81 - V.FC when handshake begins at 16800-28800 bit/second.
Hayes - Communications options
ATD$ HELP, Dial Commands USR
ATDL Dial Last Phone Number USR/Rockwell
ATDn Dial a Telephone Number
ATDSn Dial Stored Phone Number USR/Rockwell
ATEn n=0 No Command Echo
n=1 Echo Command Chars
ATFn n=0 Online Echo
n=1 No Online Echo
ATFn n=0 Best possible auto-detect, same as
n=1 V.21 or Bell 102 300bps
n=3 V.23
n=4 V.22 or Bell 212A 1200bps
n=5 V.22bis 2400bps
n=6 V.32bis or V.32 4800bps
n=7 V.32bis 7200bps
n=8 V.32bis or V.32 9600bps
n=9 V.32bis 12,000bps
n=10 V.32bis 14,400bps
n=13 V.FC 14,400
n=14 V.FC 16,800
n=15 V.FC 19,200
n=16 V.FC 21,600
n=17 V.FC 24,000
n=18 V.FC 26,400
n=19 V.FC 28,800
Rockwell, only used by V.FC modems
Clears register S31 bit 1. F13 and F19 reccommend connection rate.
ATHn n=0 On Hook (Hang Up)
n=1 Off Hook


Ati10 results Optional Features:
101=Class 1 fax
104=Class 2 fax (TR29.2)
105=Class 2.0 fax (ITU-TSS)
115=V.17 14.4k FAX
120=WorldWide support
123=Blacklisting (*B and *d commands)
124=Access Security
140=V.32bis 14.4k DATA
141=Silent Answer [fax feature]
142=Caller ID
143=MNP 10
144=MNP Cellular
146=Enhanced Config Display (\S)
147=V.FC 28k
148=Volume Control L+/L-
149=V.FC 24k
Optional Features cont.
150=Enhanced &F option
151=Enhanced Rate Renogotiation
153=ITU-TSS V.34 28.8
154=Silent Answer Plus
157=RINGING response
160=Supra Voice Porcession
161=Supra Voice Porcession
162=Supra Voice Porcession
170=Handset support
171=Headset Support
180=16550 UART emulation
181=SupraSmart UART
182=Rockwell high speed interface
190=AMD flash ROM
191=ATMEL flash ROM
ATIn n=0 Product Code
n=1 Checksum
n=2 RAM Test
n=3 Product ID string
n=4 Current Settings
n=5 NVRAM Settings
n=6 Link Diagnostics
n=7 Product Configuration
n=10 Optional features [fax, etc., see end]


ATL+/-n +n=1-32 Increases speaker volume
-n=1-32 Decreases speaker volume
Relative Speaker Volume-Optional feature #148
ATLn n=0 Low Speaker Volume
n=1 Low Speaker Volume
n=2 Med Speaker Volume
n=3 Hi Speaker Volume


ATMn n=0 Speaker Off
n=1 Speaker On Until CD
n=2 Speaker Always On
n=3 Speaker Off During Dial


ATNn n=0 Use rate in S37
n=1 Use highest possble rate
Connection Rate
ATOn n=0 Return Online
n=1 Return Online & Retrain


ATP Pulse Dial


ATQn n=0 Result Codes Sent
n=1 Quiet (No Result Codes)
n=2 Verbose/Quiet On Answer


ATT Tone Dial


ATVn n=0 Numeric Responses
n=1 Verbal Responses


ATWn n=0 Not reported, DTE rate shown
n=1 Result reported
n=2 Not reported, DCE rate shown
Error Correction Result Codes
ATXn n=0 Basic Result Codes
n=1 Extended Result Codes
n=2 Wait for tone before dialing
n=3 Ignore dial tone
n=4 Wait for tone, detect dialtone and
report busy


ATYn n=0 Next reset to &W0 settings
n=1 Next reset to &W1 settings
Internal Only
n=2 Next Reset to &F0 settings
n=3 Next Reset to &F1 settings
n=3 Next Reset to &F1 settings


ATZn n=0 Dipswitch #7 determines reset
n=1 Reset to &W0 settings
n=2 Reset to &W1 settings
n=3 Reset to &F0 settings
n=4 Reset to &F1 settings
n=5 Reset to &F2 settings
Dipswitch is USR only
AT\Nn n=0 Normal connection using flow
n=1 Direct connection, no flow control
n=2 LAPM/MNP 5,4,3, 2 (Reliable)
n=3 Autoreliable mode (LAPM or MNP)
n=4 LAPM reliable mode
n=5 MNP reliable mode
Operating Mode
AT\S Display configuration information Optional feature #146.

S Registers

S Registers Options Details
S000=n n=1-255, number of rings before the
modem answers a call


S001 Ring counter, range=0-255


S002=n Escape code, range=0-255 default=43 "+". Anything greater than 127 disables escape
S003=n range=0-127, default is 13 Carriage Return
S004=n range 0-127, default is 10 Line feed
S005=n range 0-32, default is 8 Backspace
S006=n range 2-255, default 2 or 4 Time to wait to blind dial, units=seconds
S007=n range 1-255, default=2 Time to wait for carrier, units=seconds
S008=n range=0-255, default=2 Pause time for comma, units=seconds
S009=n range=1-255, default=6 Time to wait before recognizing carrier
units=1/10 seconds
S010=n range=1-255, default=14 Delay from lost carrier to hang up
units=1/10 seconds
S011=n range=50-255, default= 70 or 95 DTMF tone duration/spacing
units=1/1000 seconds
S012=n range=0-255, default=5 Escape code guard time
units =1/100 seconds
S018=n Range: 0-255 seconds, Default: 0 Test Timer. Sets the length of time, in seconds, that the modem conducts a test (commanded by &Tn) before
returning to the command mode. If this register value is zero, the test will not automatically
terminate; the test must be terminated from the command mode by issuing an &T0 or H command.
When S18 is non-zero, the modem returns the OK message upon test termination.
S025=n range=0-255, default=1 Delay to DTR, units=1/100 seconds
S026=n range=0-255, default=5 RTS to CTS delay, units=1/100 seconds
S030=n range=0-255, default=0 Disconnect inactivity timer
units=tens of seconds
S032=n range=0-255, default=19 XON charachter
S033=n range=0-255, default=19 XOFF charachter
S036=n n=0 Disconnect
n=1 Establish a direct connection
n=3 Establish a normal connection
n=4 Establish an MNP connection if
possible, otherwise direct
n=5 Establish an MNP connection if
possible, otherwise normal
Negotiation failure treatment
S037=n n=0 Rate of last AT command issue, or
modem default (maximum)
n=1 300bps
n=5 1200bps
n=6 2400bps
n=8 4800bps
n=9 9600bps
n=10 12,000bps
n=11 14,400bps
n=12 28,800bps
Desired line speed. Ignored unless N=0, overridden by +MS setting.
S038=n range=0-255, default=20 Delay before forced disconnect
S046=n n=136 Compression disabled
n=138 Compression enabled
Protocol selection
S048=n n=0 Disable V.42, proceed with LAPM
n=7 Enable V.42
n=128 Disable V.42, look to S36
V.42 negotiation
S080=n n=0-31Reserved
n=32 V.25 commands only
n=64 Remote configure enable
n=128 Callback security enable
V.25 only, optional feature #120
default=1. Settings are bit values expressed in decimal
S086=n n=0 Normal disconnect, no error
n=4 Loss of carrier
n=5 V.42 negotiation failed
n=9 Modems could not find common
n=12 Normal disconnect initiated by
remote modem
n=13 Remote modem did not respond
after 10 re-transmissions
n=14 Protocol violation
Connection failure cause code register
S095=n n=0 CONNECT XXXX shows DCE
n=1 Append/ARQ to verbose code if
protocol is not NONE
n=2 Enable CARRIER XXXX result
n=3 Enable PROTOCOL XXXX result
n=4 Reserved
n=5 Enable COMPRESSION result
n=6 Reserved
n=7 Enable RINGING response
V.34 Rockwell Extended result codes


PSTN transit level
S095=n n=0 Disable COMPRESSION XXXX
n=32 Enable result code
USR Result code commands
S109=n n=1 reserved
n=2 4800bps
n=4 7200bps
n=8 9600bps
n=16 12000 bps
n=32 14400 bps
n=64 reserved
n=128 reserved
V.32 & V.32bis range of available modem speeds. Lowest speed to start of training/ negotiation.
S110=n n=0 V.32 no rate adjustment
n=1 V.32/V.32bis no rate adjustment
n=2 V.32/V.32bis with rate adjustment
n=3 start negotiation at lowest possible
speed as set in +MS command
n=14 V.34, V.FC, V.32bis with rate
V.32, V.32bis and V.FC rate adjustment options
S201=n n=0 initial power setting
n=5 Compromise equalizer enable
n=6 Reserved
n=7 Reserved
Cellular transmit level
Sr=n Sets Register "r" to "n"


Sr? Query Register "r"


RS-232C pin assignments










protective ground





transmit data





receive data





request to send





clear to send





data set ready





signal ground





data carrier detect





data speed indicator





transmit clock, sync only





receive clock, sync only





data terminal ready





ring indicator





data signal rate selector





external transmit clock, sync only tries to supply accurate and up-to-date information but it is possible that this page may contain typographical errors or technical inaccuracies. Any errors will be periodically corrected as they are made known to us. If any such errors are found, we would appreciate if you would report them here.
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