Hardware reference
HARDWARE REFERENCE MANUAL
268
Revision 5.0
3.13.9 Absolute encoder
SSI
SSI (Synchronous Serial Interface) is a digital system for transferring data in
serial form. SSI is the most widely used serial interface between absolute
sensors and controllers. SSI uses a pulse train from the controller to clock
out the data from the sensor.
The SSI interface of the TJ2-KS02 accepts absolute values from an encoder
if the data is in Gray Code format or in binary format and if the resolution is
25 bits or less. The number of bits, and therefore the number of clock pulses
sent to the encoder in each frame, is programmable. You set this number
with the BASIC command
ENCODER_BITS = n
.
fig. 147
When you have initialized the TJ2-KS02 with the
ENCODER_BITS
command, the TJ2-KS02 continuously sends clock pulses to the encoder.
These clock pulses are sent in frames of
n
+2 pulses, where
n
is the bit count
set. The clock rate is fixed at 200 kHz. The clock interval between frames is
32
μ
s. The resulting maximum cable length between the controller and the
sensor is 200 m.
The labels in the figure are:
A. Timing diagram.
B. Clock sequence.
C. Clock.
D. Data.
E. MSB (Most Significant Bit).
F. LSB (Least Significant Bit).
G. Clock frame.
When the data is clocked into the TJ2-MC__, the position value is
interpreted. With this position value, it produces a value for
MPOS
and a
position error that is used to close the control loop.
μ
s
32
A
B
G
G
C
D
E
F
