R02192
Matching Module 4 for Absolute Encoders
I
7.3.1.2 Gray Code
till
Maximum resolution = 20 bits + 1 control bit
Encoders with a higher resolution, indicating the respective number of TBs, can be also con-
nected, but the module will only evaluate up to 20 bits (Fault message by sign–bit VZ = 1 (i.e.,
overflow + synchronization bit = O).
The actual values from the gray code encoder are converted to binary code on the encoder match-
ing module and are transferred to the basic module via the output memory (Solder in jumper
BR1
for “Gray”).
Offset value K must be considered for encoders with symmetrically capped gray code. The offset
value is calculated as follows:
n = Number of bits required to represent the maximum desired binary number
(e.g., 9 bits for the number 359)
s = Desired step number (e.g., O to 359 = 360 steps)
Our example has an offset value of
K
=
29
–
360
=
512
–
360
= 76.
2
2
Thus, the encoder will give the value 76 instead of “zero”. The area end value is then
76 + 359 = 435.
Encoders with an additional control bit can be evaluated if the control bit is transmitted in the last
position (after the LSB) (see “The Time Sequence of a Read Cycle” example in section 7.1).
7.3.1.3 BCD Code
Maximum resolution = 5 decades + 1 control bit
Without being converted on the encoder matching module, the actual values are directly trans-
ferred to the basic module via the output memory. (When their setpoints are presented in binary
code, the processing time of the basic module must be taken into account.) Solder in jumper
BR1
for “BCD/BIN”.
1P
241 Equipment Manual
@
Siemens
AG 1989, Order No.: 6ES5 998-0KD21
7–7
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