Data Formats; Faulty Ssi Query - Balluff BTL7-S5 Série Notice D'utilisation

BTL7-S5 _ _ D-M _ _ _ _ -T _ 2/3-S32/KA _ _ /FA _ _
Magnetostrictive Linear Position Sensor – Rod Style
6
SSI interface (continued)
6.2

Data formats

The BTL is factory set as following for position output:
– 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. Position, velocity or
position/velocity differences can be sent on the Data line.
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. Negative values are output in 2's
complement. With positive velocities, the magnet moves
away from the electronics head; with negative velocities it
moves towards the electronics head. The controller must
then be set to processing of signed data.
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, the data output goes to
o
Low and after time t has elapsed to High. The high level is
m
maintained until the next clock burst. Time t
time t .
o
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 reset for every additional edge
m
of Clk and internally the T event is set. After time t
m
data again goes to High.
www.balluff.com
5 6 7 8 9 10
12 11 10 9 8 7
= 2 · T timeout times)
o Clk
following
m
the
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 here is 21 bits, the total bit
number is 26. Four zeros are sent 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
o m
communication error in the BTL7 Configuration Tool. In
summary a communication error can have the following
causes:
– 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 clock pause between two clock packets is too
short
→ T
event
m
Position
17
0
LSB
event
english
0
L
0
15