3Com Courier, Reference, Page: 143 / 204

A
S-R
EGISTERS
Understanding
Bit-Mapped
S-Registers
A bit-mapped S-Register uses one number to describe a collection of
settings. Bit-mapping allows us to pack a lot of information in a small
space.
Bit-mapped registers are in the form of Sr.b=n, where r is the bit-mapped
register;.b is the bit; n is 0 (off) or 1 (on).
The modem displays the value of an S-Register, as a decimal value
between 0 and 255. The modem, however, understands the decimal
value as a collection of binary digits (bits).
How bits are
mapped to decimal
values
Bits can be mapped into decimal values. Each bit can be either on (1) or
off (0). Eight bits create 256 unique combinations of 1s and 0s. Each of
the eight bits can be assigned a number corresponding to its position:
b b b b b b b b
7 6 5 4 3 2 1 0
Also, each bit can be assigned a value corresponding to its number:
Bit Value
7 2
7
= 128
6 2 6 = 64
5 2
5
= 32
4 2 4 = 16
3 2
3
= 8
2 2 2 = 4
1 2
1
= 2
0 2
0
= 1