CIRCUTOR CVMk2 Series - Manual (Page 123)

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CVM k2
OPERA
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CVM k2
COMMUNICA
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8. COMMUNICATIONS
8.1. MODBUS/RTU PROTOCOL ©
CVMk2 uses the Modbus/RTU © as the communications protocol on the COM2 port. This is a
question-response based protocol. The question frame format is:
NPAAXXXXYYYY CRC.
PN: The number of the peripheral configured for the system.
AA: Modbus function to be executed.
XXXX: System's memory position where the function should be begin. (Example: If AA=04 the
function is read only).
YYYY: Read positions, from the XXXX position, to be read or written. (This depends on the AA
function).
CRC: Code for detecting 16 bit errors. (automatically generated).
The response format is
NPAABBCCCC..CRC
PN: Number of the peripheral that responds
AA: Function that responds.
BB: Number of bytes in the response.
CCCC: Registry value.
...
CRC: Error detection registry.
For more information, see the standard Modbus© protocol.