Temposonics
®
R-Series
V
SSI
Operation Manual
I 23 I
5. Commissioning
5.1 Introduction
SSI
The synchronous-serial interface (SSI) is a digital interface that en-
ables serial transmission. Data is transmitted from the device to the
connected control system synchronously to a clock rate specified by
the control system. The interface of Temposonics
®
position sensors
corresponds to SSI industry standard for absolute encoders. Its dis-
placement value is encoded in a 24/25/26 bit binary or gray format
and transmitted as a differential signal in SSI standard
(RS-485/RS-422) – independent of data width of the code (resolu-
tion). The absolute, parallel position data is continually updated by the
sensor and converted by the shift-register into a serial bit stream. De-
pendent on the baud rate chosen in the control system the following
cable lengths are possible:
Logic diagram
Sensor
Controller
Clock (+)
Clock (−)
Optocoupler
Driver
Data (+)
Data (−)
+24 VDC
0 V
ASIC for parallel and absolute position data
Microprocessor system
position value = 24/25/26 bit
binar
y or gray
Shift register
parallel serial converter
Sensor input
100 Ω
7 mA
Clock (+)
100 Ω
LED
100 Ω
Clock (−)
100 Ω
Optocoupler
1.6 V
1 nF
1 nF
Cable length
< 3 m
< 50 m
< 100 m
< 200 m
< 400 m
Baud rate
1 MBd
< 400 kBd
< 300 kBd
< 200 kBd
< 100 kBd
Clock T
Standard
one shot
n * T
MSB: Bit n
Bit n - 1
Bit 3
Clock
Data
High
Low
High
Low
LSB: Bit 1
Bit 2
1
2
3
4
5
6
The data is transferred serially at SSI, whereby the control system de-
termines the time of the polling. During data transmission, the proce-
dure described below is carried out (Fig. 32):
1. In the idle state, when no data is transmitted, the data line and the
clock line are at high level.
1
2. The current position data is frozen in the shift register with the
first falling clock edge. It is no longer possible to update the
position data in this cycle.
2
3. The bit is applied at the following rising edge.
3
4. With the following falling edge, the transmission of the data
begins with the
M
ost
S
ignificant
B
it (MSB).
4
5. This is repeated for each next lower bit until the
L
ast
S
ignificant
B
it (LSB) is transmitted.
6. The standard one shot starts after the last falling clock edge
5
.
After the transmission of the LSB, the data line remains on the
low level and the clock line on the high level until the end of the
standard one shot. Then the sensor is ready for the transmission
of a new data
6
.
Fig. 29: Cable lengths and related baud rates
Fig. 30: Schematic connection
Fig. 31: Input wiring clock (+)/clock (−)
Fig. 32: Timing diagram
