Quatech RS-422 - Manual (Page 17)

4.5 Options Register
The Options Register allows software to identify the DSCLP-200/300 as a
Quatech Enhanced Serial Adapter. It also allows software to set the UART clock rate
multiplier. Figure 10 shows the structure of the Options Register.
The powerup default of the Options Register is all bits zero.
Clock rate multiplier bit 0 RR0 0
Clock rate multiplier bit 1 RR1 1
(reserved, 0) - 2
(reserved, 0) - 3
(reserved, 0) - 4
(reserved, 0) - 5
ID bit 0 ID0 6
ID bit 1 ID1 7 (MSB)
Description Name Bit
Figure 10--- Options Register bit definitions
4.5.1 Enhanced Serial Adapter Identification
The ID bits are used to identify the DSCLP-200/300 as a Quatech Enhanced
Serial Adapter. Logic operations are performed such that the values read back from
these bits will not necessarily be the values that were written to them. Bit ID1 will return
the logical-AND of the values written to ID[1:0], while bit ID0 will return their
exclusive-OR.
Software can thus identify a Quatech Enhanced Serial Adapter by writing the
ID bits with the patterns shown in the "write" column of Figure 11, then reading the bits
and comparing the result with the patterns in the "read" column. Matching read patterns
verify the presence of the Options Register.
0 1 1 1
1 0 0 1
1 0 1 0
0 0 0 0
ID0 ID1 ID0 ID1
Read Write
Figure 11 --- ID bit write/read table
12 DSCLP/SSCLP-200/300 User's Manual