dCS 904 User Manual | Manual for Software Version 1.5x and 1.36 |
dCS Ltd | June 2000 |
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The system employs the following protocol - all transactions are initiated by the PC. The PC is the transmitter and units on the daisy chain are receivers.
Byte 1 : ID of unit to process command
Byte 2 : Command (single byte)
Byte 3 : Length of parameter string
Byte 4 : List of parameters
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Last byte : Checksum of parameter list
The minimum length of a transmit message is 4 bytes, maximum 64 bytes, limited by a buffer within the receiving unit. There are two cases for parameter length mismatch.
(a) Receiver expects n parameters, transmitter sends more.
This condition may arise when a later version remote tries to communicate with an earlier version of receiver. The receiver acts on first n parameters in list, ignores rest. The full parameter list is check summed.
(b) Receiver expects n parameters, transmitter sends less.
This condition may arise when a earlier version remote tries to communicate with an later version of receiver. The receiver acts on all parameters in list, and uses sensible defaults for the rest (ideally, no action except where this is silly). Do not truncate a command sequence expecting the receiver to do something sensible. The full parameter list is check summed.
The checksum is the sum of the bytes in the parameter list (bytes 4 to
The addressed receiving unit (ADC, DAC, DDC, Master Clock, etc) acknowledges within 50 msecs of the last transmitted byte in the transmit message. For some special cases (dCS use only, see “Special Commands and Protocols” below) commands do not acknowledge. If the checksum is incorrect the receiving unit will ignore the command, clear its buffer and will not acknowledge. Only valid command bytes will generate an acknowledge, other command bytes will be ignored, clearing the receiver buffer.
The acknowledge response starts with:
Byte 1 : 101010xx – indicates successful transmission to physical address, with xx indicating the time the unit may take to respond to the command
and then, with a command dependant part:
Byte 2 : ID of unit that processed command
Byte 3 : Command (single byte)
Byte 4 : Length of response string
Byte 5 : List of response bytes
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Last byte : Checksum of response list
Manual part no: DOC135904 iss 2B2 | Page 54 | 135904ma2b2.pdf file available from website |
Contact dCS on + 44 1799 531 999 | email to: more@dcsltd.co.uk |
(inside the UK replace + 44 with 0) | web site: www.dcsltd.co.uk |