Quatech RS-422 user manual Options Register, Enhanced Serial Adapter Identification

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.

Bit	Name	Description
7 (MSB)	ID1	ID bit 1
6	ID0	ID bit 0
5	-	(reserved, 0)
4	-	(reserved, 0)
3	-	(reserved, 0)
2	-	(reserved, 0)
1	RR1	Clock rate multiplier bit 1
0	RR0	Clock rate multiplier bit 0

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.

Write		Read
ID1	ID0	ID1	ID0
0	0	0	0
0	1	0	1
1	0	0	1
1	1	1	0

Figure 11 --- ID bit write/read table

12 DSCLP/SSCLP-200/300 User's Manual