Maxim Integrated Teridian V.22 bis Linux Softmodem for 73M1822/73M1922 MicroDAA - Manual (Page 63)

UG_1x22_043 V.22 bis Linux Softmodem for 73M1x22 MicroDAA User Guide
Rev. 1.5 63
SMS Applications
The TSC Softmodem has been optimized for SMS and V.23 half duplex in general. There
are several enhancements that have been added to the TSC Softmodem to make it more
compatible with SMS, including faster turn around and demodulator settling. Normally the
modem will be used in the “clear channel” mode (Y0), but this is not mandatory. Speed
buffering (Y6) at 4800/9600bps using XON/XOFF (K4) can also be used instead of Y0 and
1200bps. RTS/CTS (K3) flow control cannot be used because these signals are being
used to control the V23HD carrier. The TSC Softmodem modem is typically initialized with
the command string: ATY0B10S73-32C2S10=255 this is broken out as follows:
Y0
clear channel mode (1200 bps)
B10 V.23 HDX gated by RTS
S73-32 no 125ms wait between commands
C2 DCD follows the raw received carrier
S10=255 disable loss of carrier timeout
The following two sequences are typical of how the TSC Softmodem should be used in a
communications session. A SMS session can be quite complicated as described in the
referenced documentation, so this example should not be interpreted to be all that is
required. There are various signal times and time-outs that also need to be observed and
these all have there own decision trees that need to be accounted for.
Polling of CTS-DCD signals is necessary. CTS indicates that modem is ready to send data.
DCD indicate that receive data is valid. CTS, DCD and RTS are all low true signals at the
RS232.
RTS-ON to CTS-ON response time is controlled by S90 (range 10ms to 2.55s).
RTS-OFF to CTS-OFF is <4ms
Using C2 carrier option, DCD will turn on after receiving carrier for 10-20ms.
Case 1: SM-TE TSC Softmodem (Master) to SM-SC (Slave) transmission sequence
for a SMS message
1. Set the Local Host serial data rate to 1200bps
2. The Local Host controls the V23 carrier with RTS signal
3. Turn off RTS (to start modem as a receiver and prevent sending carrier)
4. Send ATY0B10S73-32C2S10=255 to initialize the TSC Softmodem modem
5. ATDTnnn.. (TE dials SMS-SC)
6. Modem will display "Connect 1200" with CTS off and DCD off
7. Modem waits for V23 carrier from SM-SC
8. Wait for DCD on (SM-SC carrier received)
9. Detect channel seizure and mark from V.23 receive data
10. Wait for DLL_SMS_EST signal and DCD turn off (SM-SC switched to receive
mode)
11. Turn on RTS (to switch modem to transmit mode)
12. Wait for CTS on to indicate TSC Softmodem is ready to send data
13. Transmit DLL_SMS_INFO_MO originate message to SM-SC
14. Turn off RTS (to switch modem to receive mode)
15. Wait for DCD on (SM-SC carrier is being received)
16. Detect ACK1 message from SM-SC or time-out. The slave will include the TL
confirmation or rejection message in the payload, or a null message if the timer
expires.
17. Wait per SMS timing and DCD turn off (SM-SC switched to receive mode)