Operating instructions

Absolute Rotary Encoders
67
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Absolute Encoders BVS58/BVM58 Series
Programming (continued)
Position data
Slave A Slave B Slave C Slave D
XXX0 XXX0 XXX0 XXX0
XXX1 XXX1 XXX1 XXX1
XXX0 XXX0 XXX0 XXX0
XXX1 XXX1 XXX1 XXX1
Cycle
1
2
3
4
etc.
Slave A
Data bit D2
0
1
0
1
Operating Modes
Address assignments for the four slaves
The AS-Interface master accesses all slaves sequentially within an AS-Interface cycle to transfer output data to slave A or
to read input data from the slaves. The single-turn absolute encoder uses four AS-Interface chips to transfer a position of
13 bits using 4 slave addresses.
These four slaves are queried sequentially and data may originate from any one of four different sampling times. To
minimize this effect, sequential addresses (n, n+1, n+2 and n+3) should be assigned to slaves A, B, C and D.
In addition, slave A is responsible for controlling the encoder’s functions. If the order of slaves is changed (D=n, C=n+1,
B=n+2, A=n+3), the output word, which is supposed to be transmitted by the function control module of the absolute
encoder, will not be transmitted until slaves D, C and B have been read in. A memory command would then only take effect
for slave A. The command would not affect the slaves that had already been read until the next read cycle. This change of
slave order will result in data inconsistency.
Temporary storage and transfer with flag bits
If any data from the rotary encoder is interrupted during transmission, it is possible that some of the data transferred to the
controller originates from a different position in the data word. The controller can check the data integrity for a single data
word by comparing the four flag bits. Each slave can transfer one flag bit making it possible for the control module to check
which position data set an individual data set belongs to by comparing the 4 bits. Data bit D2 is used for this purpose.
Using the flag bits reduces the size of the usable data from 16 bits to 12 bits.