Parker
Hannifin
Overview
SSI (Synchronous Serial Interface) is a unidirectional synchronous serial link
for retrieving predefined data from a slave device. The ACR9000 (or
ACR9030) Stand-Alone Controller drives one differential signal out to a slave
device, and receives one differential signal from the slave device: SCLK
(clock out) and SDATA (data in). The slave device latches new data on the
first falling edge of SCLK. The slave responds by synchronously shifting the
data out using the SCLK rising edge to assert SDATA.
As implemented in the ACR9000 (or ACR9030) controller, the general
characteristics of the SSI are:
•
Physical layer is RS-485.
•
Network topology is point-to-point, single master/slave.
•
Data rate is 97.6 KHz to 1.56 MHz.
•
Message frame size is 1 to 32-bits.
•
Selectable data modes are gray code to binary conversion or
pass-thru mode.
Protocol
Slave Device
When not transmitting, the SCLK and SDATA lines are high. The slave
device latches a new data value on the first falling edge of SCLK. It then
transfers the latched data value out on the subsequent rising edges of SCLK
(MSB first). After the transfer completes, the SDATA line remains logic low
for a period defined by the slave device. If the slave device detects a falling
edge SCLK before the SDATA line is high, the slave device retransmits the
same data value on the subsequent rising edge SCLK.
Master Device (ACR9000 and ACR9030 Controllers)
The ACR9000 and ACR9030 controllers initiate a new SSI transfer at the
beginning of a servo period by generating SCLK. The controller then qualifies
subsequent data values on SDATA using the rising edge of SCLK.
110 ACR9000 Series Hardware Installation Guide
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Summary of Contents for ACR9000
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