1 U8480 Series Remote Operation
58 U8480 Series Programming Guide
How to read registers
The condition polling method is used to access the information in the status
register groups. In this method, the U8480 Series has a passive role. It only
informs the PC that conditions have changed when the PC “asks”. When you
monitor a condition with the polling method, you must:
1 Determine which register contains the bit that monitors the condition.
2 Send the unique query that reads that register.
3 Examine the bit to see if the condition has changed.
The polling method works well if you do not need to know about the changes the
moment they occur. Detecting an immediate change in a condition using the
polling method requires your program to continuously read the registers at very
short intervals. This is not particularly efficient, and there is a possibility that an
event may be missed.
Status registers
The Status System in the U8480 Series is shown in Figure 1-13. The Operation
Status and Questionable Status groups are 16 bits wide, while the Status Byte and
Standard Event groups are 8 bits wide. In all 16-bit groups, the most significant bit
(bit 15) is not used and is always set to 0.
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