73m2901ce Maxim Integrated Products, Inc., 73m2901ce Datasheet - Page 16

• Manufacturer Part Number: 73m2901ce
• Description: V.22bis Single Chip Modem
• Manufacturer: Maxim Integrated Products, Inc.

73M2901CE Data Sheet
6.4
6.4.1 SMS and V.23 Half Duplex
SMS (Short messaging Services) is the communications mode used to transmit text messages for cell
phones and eventually wire line phones as well (see the 73M2901CE SMS and Half Duplex V.23
Operation application note). The V.23 half duplex mode has been included with the addition of the B10
command (ATB10). The B10 command allows the used to turn the transmitter on and off using the serial
interface RTS signal. In this way the modems can easily communicate in half duplex mode using RTS to
enable transmission and CTS to indicate the modem is ready to send data. The V.23 receiver response
time has also been improved to allow for fast line turnaround (reversal of the data flow). The pattern
generator has also been modified to send the proper alternating pattern used in the SMS handshake.
SMS messaging is very similar to the format used for Caller ID, so the 2901CE can also be used to send
Caller ID messages to equipment designed to use and display Caller ID information. A typical command
line for a dial up connection would be: ATY0B10S73-32C2R2S10=255<CR>. These commands are
broken out as follows:
Y0
B10
S73-32
C2
R2
S10=255
Note that RTS/CTS flow control cannot be used when using V.23 half duplex since RTS is used to turn
the carrier on and off. XON/XOFF flow control should be used instead if flow control is needed. The
transmitter RTS to carrier on delay time is 10mS and the off delay is 5mS.
6.4.2 Leased Line Mode
One of the drawbacks to the earlier 73M2901 modems is that they are designed primarily for dial-up
modem applications. This made it difficult to use them in some non-dial-up designs. The 73M2901CE
adds a leased line mode that allows a modem to go into the data mode without having to go through a
normal handshake or the need for a connection to another modem. The leased line mode is enabled
using the @L1 command in the initialization string. The 73M2901CE leased line mode should not be
thought of as limited to only leased line. It is also suited to radio links and any applications where the
modem needs to be ready to go when it is first connected. Leased line mode can be used with all
modulation modes that are supported by the 73M2901CE. Table 1 shows typical command initialization
strings that can be used.
16
Functional Considerations
V22bis LL
V22 LL
B212 LL
B103 LL
B202 RX LL
B202 TX LL
V23 HDX LL
V23 TX1200 LL
V23 TX75 LL
V21 LL
Clear channel mode (1200 bps)
V.23 HDX gated by RTS
No 125mS wait between commands
DCD follows the raw received carrier
Toggle DTR to hang up
Disable loss of carrier timeout
Table 2: Leased Line Initialization Commands
ATFS99=1Y6K3C1R2S30=4S70=12S26+4O2@L1
ATFS99=1Y6K3C1R2S30=8@L1
ATFS99=1Y6K3C1R2S30=16@L1
ATFS99=1Y6K3C1R2S30=32@L1
ATFS99=1Y6K3C1R2B4@L1
ATFS99=1Y6K3C1R2B5@L1
ATFS99=1Y0C2R2B10@L1
ATFS99=1Y6K3C1R2B3@L1
ATFS99=1Y6K3C1R2B2@L1
ATFS99=1Y6K3C1R2S30=64@L1
DS_2901CE_031
Rev. 3.4