AV6A 19
SSI Protocol “S”
The SSI Protocol “S” provides a clocked set of data bits that
represent the encoder position (in turns and within 1 turn). Each bit
is output by the encoder as the clock input transitions.
Preferred cable: Twisted pair with individual and overall shield
grounded at one end only. 24 AWG, copper conductor, capacitance
of 52.5 pF/meter (16 pF/foot) terminated in a 100 Ohm resistive
load. Note that resistive losses in long cables may decrease actual
voltage (+Vs) available at the encoder; larger conductors can be
used or the encoder can be powered locally and signal GND brought
through the cable. Maximum transmission speed is limited by cable
length as shown in the figure below.
For more details on SSI, consult Wikipedia:
http://en.wikipedia.org/wiki/Synchronous_Serial_Interface
Set Zero
(input, ACTIVE HIGH, Falling Edge, 10K resistance)
To set the encoder count value to zero, raise Set Zero> 10V, < Vs for
more than 1 second. Upon the Set Zero signal returning to logic zero
(falling edge), the encoder count value will be set to zero.
Set Direction
(input, 10K resistance)
For input logic zero or no connection, the encoder will count UP for
CCW rotation as viewed from the rear end of the encoder.
For input logic 1 (>10V, <Vs), the encoder will count DOWN for CCW
rotation as viewed from the rear of the encoder.
SSI TROUBLESHOOTING
For SSI, monitor the clock input line to ensure the controller is
triggering the encoder to send position. The clock should obey the
signal requirements shown in the SSI signal section, and should
appear as a rapid set of transitions on the clock line. The encoder
data transmit lines should change state as data is clocked out. Note
that the varying binary patterns representating position can produce
pulses of varying width--this is normal.
SSI Diagnostic LEDs
LED
Status
Meaning
PWR
Green
Power OK, Status OK
Off
No Power or
Preset Button Pressed
ALARM
Off
Status OK
Red
Internal Fault
(All output bits are set =1)
10K
10K
1K
100
10
1.2K
100K
1M
10M
DATA SIGNALING RATE - bit’s
Cable Lenght versus data signaling rate
CABLE LENGTH - METERS
