Data Formats; Faulty Ssi Query - Balluff BTL7-S5 M Serie Betriebsanleitung

BTL7-S5 _ _ ( _ )-M _ _ _ _ -A/B/Y/Z(8)-S32/S115/S140/S147/KA _ _ /FA _ _
Magnetostrictive Linear Position Sensor — Rod Style
6
SSI interface (continued)
6.2

Data formats

The SSI Standard BTL is factory set as following for
position output, which can no longer be changed
retroactively:
– SSI24, SSI25 or SSI26
– Binary or Gray coded
– Rising or falling
The contents of the information to be transferred and the
error value can be configured with the BTL7-S510....
Position, speed, or position/speed differences can be sent
via Data. The MSB is always transmitted first.
SSI16
Clk
1 2 3 4
Data
15 14 13
MSB
Fig. 6-1: Example of a complete SSI16 data transmission
Depending on the configuration, position or speed data
may have a leading sign with the BTL7-S510.... Negative
values are output as a two's complement. With positive
speeds, the magnet moves away from the electronics
head; with negative speeds it moves towards the electro-
nics head. The controller must be set to process signed
data then.
6.3

Faulty SSI query

Underclocking
If there are too few clock edges, the current data level will
be maintained for the time t (t
o
after the last negative edge from Clk. If, however, another
positive edge occurs, the next bit will then be output.
Afterwards, a T event will occur internally, the data output
o
switches to low and then back to high after the time t
elapsed. The high level is maintained until the next clock
burst. Time t starts after the end of time t
m
Overclocking
If there are too many clock edges, the data output will
switch to low after the correct number of cycles has been
completed. The t timer is started again for every
m
additional negative edge from Clk and the T
internally. Data switches back to high after the time t
elapsed.
www.balluff.com
5 6 7 8 9 10
12 11 10 9 8 7
= 2 · T Timeout times)
o Clk
has
m
.
o
event is set
m
has
m
23
M
Output of a position via SSI24
M = MSB (Most Significant Bit)
L = LSB (Least Significant Bit)
25 24 23 22 21 20 Error value or position value
0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Example of a SSI26 with error bit at bit position 21 and
error value 0. The data length there is 21 bit, the total bit
number is 26. Four zeros are transmitted before the error
bit.
11 12 13 14 15 16
6 5 4 3 2 1
A T or T event is displayed in the status field as a com-
o m
munication error in the BTL7 Configuration Tool. In short, a
communication error is caused by the following:
– The bit number set in the BTL does not correspond to
the bit number in the controller.
n > n  T event
BTL PLC o
n < n  T event
BTL PLC m
– The SSI clock frequency is too low
f < 9.771 kHz  T
Clk o
– The pause between two clock packages is too short
event
 T
m
Position
17
0
LSB
event
english
0
L
0
15