Pepperl+Fuchs WCS Series User Manual

2020-01
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WCS* Read Head Position Encoding System
SSI Interface (LS3xx*)
5.3 Data Protocols
The read head with SSI interface supports data formats in gray code (LS311) or binary code
(LS310). Data transfer for the SSI read head is carried out on request from the control panel.
SSI interface
The clock signal (CLK) generated by the control panel is used for the transfer. If no data trans-
fer begins, the serial data output of the read head remains at 1. The data transfer begins with a
falling edge of the clock signal. With each rising edge of the clock signal, the read head trans-
mits one bit of the current position. The transfer begins with the most significant bit (MSB) and
ends with the least significant bit (LSB).
Figure 5.4 SSI data format
The read head with SSI interface corresponds to a 19-bit absolute encoder in the data format.
Effectively, the WCS read head delivers up to 512 revolutions and 1024 increments/revolution.
The clock rate between the control panel and the read head may be 100 ... 1000 kHz. The rec-
ommended value is 250 kHz.
Bit 1 ... 3
The first three bits are always 0.
Bit 4 ... 22 (2
18
... 2
0
position values)
The position values are transferred to bits 4 to 22 of the SSI protocol. For LS311 read heads the
position values are gray encoded, and for LS310 read heads the position values are binary
encoded.
Bit 23 (OA read head outside the code rail)
A distinction is made between two different states:
1. The code rail is located in the read head gap, but outside the possible tolerances. In this
case, the control panel receives the following bit pattern:
KB = 0
OA = 0
POS 2
0
... 2
18
= 1 (position value 524287)
2. There is no code rail in the read head gap. In this case, bit OA = 1 (Out All) is set in addi-
tion to the above bit pattern.
0 0 0 2
18
2
17
2
16
2
15
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
OA DB KB
MSB
LSB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
CLK
BIT
DATA
Note
Position data (bit 4 ... 22) are output for LS311 read heads in gray code. Status and error bits
(bit 23 ... 25) are not output in gray code.

Pepperl+Fuchs WCS Series Specifications

General

Brand	Pepperl+Fuchs
Model	WCS Series
Category	Media Converter
Language	English