Parker HannifinOverviewSSI (Synchronous Serial Interface) is a unidirectional synchronous serial linkfor retrieving predefined data from a slave device. The ACR9000 (orACR9030) Stand-Alone Controller drives one differential signal out to a slavedevice, and receives one differential signal from the slave device: SCLK(clock out) and SDATA (data in). The slave device latches new data on thefirst falling edge of SCLK. The slave responds by synchronously shifting thedata out using the SCLK rising edge to assert SDATA.As implemented in the ACR9000 (or ACR9030) controller, the generalcharacteristics 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 orpass-thru mode.ProtocolSlave DeviceWhen not transmitting, the SCLK and SDATA lines are high. The slavedevice latches a new data value on the first falling edge of SCLK. It thentransfers the latched data value out on the subsequent rising edges of SCLK(MSB first). After the transfer completes, the SDATA line remains logic lowfor a period defined by the slave device. If the slave device detects a fallingedge SCLK before the SDATA line is high, the slave device retransmits thesame 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 thebeginning of a servo period by generating SCLK. The controller then qualifiessubsequent data values on SDATA using the rising edge of SCLK.110 ACR9000 Series Hardware Installation Guidewww.comoso.com
