Si2401
Preliminary Rev. 0.9
25
send the first SIA block after the “c” is received. Once
the block is transmitted, the modem can monitor for the
acknowledge tone by completing the following
sequence:
1. Place the Si2401 in the command mode by pulsing the
ESCAPE pin (Si2401 pin 14). The “+++” and “ninth-bit”
escape modes operate in the “!2” mode but are not
recommended because they can send unwanted
characters to the remote modem.
2. Issue the “ATX1” command to turn the modem transmitter
off and begin monitoring for the acknowledgment tones.
3. Monitor for a positive (negative) acknowledgment “P” (“N”)
after the tone has been detected for at least 400 ms.
4. The modem, still in command mode, can be placed online
as a transmitter by issuing the “ATX2” command or a
receiver by issuing the “ATX3” command. If tonal
acknowledgement is not used, the host can toggle the
ESCAPE pin to place the Si2401 in the command mode
and issue an “ATX2” or an “ATX3” command to reverse
data direction.
This sequence can be repeated for long messages.
Modem Result Codes and Call Progress
Table 14 shows the modem result codes that can be
used in call progress monitoring. All result codes are a
single character to speed up communication and ease
host processing.
Table 14. Modem Result Codes
Command
Function
a
British Telecom Caller ID Idle Tone
Alert Detected
b
Busy Tone Detected
c
Connect
d
Connect 1200 bps (when pro-
grammed as V.22bis modem)
f
Hookswitch Flash or Battery Reversal
Detected
H
Modem Automatically Hanging Up in
!2, !1
I
Intrusion Completed (parallel phone
back on-hook)
i
Intrusion Detected (parallel phone off-
hook on the line)
K
Kissoff Tone Detected
k
Contact ID Kissoff Tone too long (!1)
L
Phone Line Detected
l
No Phone Line Detected
m
Caller ID Mark Signal Detected
N
No Carrier Detected
n
No Dial tone (time-out set by CW
[S02])
O
Modem OK Response
R
Incoming Ring Signal Detected
r
Ringback Tone Detected
t
Dial Tone
v
Connect 75 bps TX (V.23 originate
only)
x
Overcurrent State Detected After an
Off-Hook Event
^
Kissoff tone detection required
,
Dialing Complete