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MODEM 325 AND MODEM 325 CARD
Most users can skip this chapter. Your communications software, or the AT commands described in
, will be enough to configure your modem for everything you need it to do.
Chapter 6
However, manipulating the status registers (usually called "S-registers") directly gives programmers
more sophisticated capabilities. This chapter explains what the S-registers are and how to use them to
change the configuration of the modem.
7.1 How S-Registers Work
The S-registers hold all the modem's configuration information. When you send—or your software
sends—an AT command to change the configuration, the AT command changes a number in one of the
S-registers.
You can also change the S-registers directly by "writing" to them—using ATS commands to change the
numbers stored in the registers. Except for certain "read-only" registers, which cannot be changed by
ATS commands, every S-register can be manipulated this way.
See
for a complete list of the modem's S-registers.
Appendix D
Bit values for S-registers must not be confused with the total register value. In some S-Registers, bit
values are counted separately for each option group (a technique called bit-mapping), while the register
value is the cumulative decimal or hexadecimal total. The decimal value counts all eight bits as a single
group. Hexadecimal values split the bits into two groups of four each. Writing to an S-register changes
the total value.
illustrates the difference between decimal calculation and hexadecimal calculation.
Figure 7-1
Bit
Decimal Value
S22 Value
Decimal Total
Hexadecimal Value 8
S22 Value
Hexadecimal Total
9 6
7. Status Registers
7
6
5
4
128 64
32
16
0
1
0
0
64
4
2
1
0
1
0
0
4
and
Figure 7-1. Calculating S-Register Values.
3
2
1
0
8
4
2
1
0
1
1
0
+
4 + 2
8
4
2
1
0
1
1
0
4 + 2
= 70
= 46
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