JVL MAC050 - Using External SSI Encoder

JVL A/S - User Manual - Integrated Servo Motors MAC050 - 4500 55
2.11 Using external SSI encoder
2.11.1 SSI Encoder
SSI support is added to the MAC50-141-A series of servomotors, this feature is very use-
ful to determine the absolute position of the motor shaft if an encoder is connected di-
rectly to this or another encoder position.
The SSI interface
When the differential lines are used for SSI, the A1+/- lines work as a Clock signal from
the motor to the encoder, while the B1+/- signals work as a Data signal from the encod
-
er to the motor.
The figure above shows the SSI protocol principle. The Clock line is normally high. When
a reading is requested, the Clock goes low for t
1
micro seconds to allow the encoder to
sample and prepare a value. On the first rising edge of the Clock (1), no sampling is done,
but on the second rising edge of the Clock (2) the first data bit is read from the Data line.
Shortly after reading the bit value, the motor will set the Clock high and execute another
cycle, where the data bit is sampled just before each rising Clock. After the last data bit
has been sampled, the Clock stays high.
In the MAC-motor several registers are available for storing values for different purpos-
es. Position registers P1-P8 (available from MacTalk etc.) are used to hold SSI positions.
Only MAC050 to 141-A
The FastMac
commands field
TT1155GB
SSI Control
section
Input/Output
setup
Power
management
TT1158GB
n*T
t
1
T
t
3
t
2
a
1213
n+1
n
n-1
1
0
MSB
LSB
CLOCK
DATA