User`s manual

APPENDIX E – ANALOG I/O MEZZANINE CARD E-4
CDS7324 (FORMERLY LSF-0819)
Rev. A INSTALLATION & USER’S MANUAL
Clock In
Data Out
E.5 SSI Interface
The SSI (Synchronous Serial Interface) protocol is a point to point configuration with only transmission
capabilities. Its output is configurable via Moog GUI software only. Refer to specific application manual for more
details on this topic.
The SSI protocol is asynchronous and stateless. The SSI protocol command structure consists of three parts:
• a header
• a payload
• an optional CRC checksum
Figure E6 SSI Protocol
The SSI protocol byte order is Big Endian (most significant byte first).
The SSI Interface requires a clock pulse from the external controller. The input frequency of the Clock In pulse
determines the rate at which the Data Out will output the serial information. The data is strobed out on the
positive edge of the clock. The format of the message will be in standard binary format.
Figure E7 Clock and Data Out
The frequency of the clock pulse is limited by the length of the conductor used. The following table gives a rough
estimate of max clock frequency per cable lengths as this may vary with cable type. Please refer to specific
controller device manuals for specific information.
Clock rate
(kHz)
Cable Length
(ft)
150 600
230 400
250 360
375 240
Figure E8 Clock Speed and Cable lengths
The data bits will be streamed in a word of 32 bits. The controller must be setup for this streaming output.
E.5.1 Interface
See Figure E9
Length ~Length Payload CRC Start