Hardware reference
HARDWARE REFERENCE MANUAL
149
Revi
si
on 3.0
3.8.6
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 TJ1-FL02 accepts absolute values from an
encoder if the data is in Gray Code format or in binary format and if
the resolution is 24 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. 93
When you have initialized the TJ1-FL02 with the
ENCODER_BITS
command, the TJ1-FL02 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 TJ1-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.
The connections for SSI are:
/i
μ
s
32
A
B
G
G
C
D
E
F
Encoder signal
Axis A
Axis B
DATA+
6
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I51E-EN-03.book Seite 149 Donnerstag, 28. Juni 2007 1:05 13
