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7 MODBUS PROTOCOL
b) READ INPUT REGISTERS, FUNCTION CODE 04
Modbus Description: Reads the binary contents of the input registers in the MDP relay.
The actual values available on the MDP are: Relay Status, Phase currents, Ground currents, Phase Trip cur-
rents, ground trip currents, and trip time.
•
QUERY: The query message specifies the starting register and the quantity of the registers to be read.
Registers are addressed starting at zero; i.e., registers 1 to16 are addressed as 0 to 15
•
RESPONSE: The register data in the response message are packed as two bytes per register, with the
binary contents right justified within each byte. For each register the first byte contains the high order bits
and the second contains the low order bits.
Data is scanned in the MDP at a rate of 125 registers per scan. In response to this command from Host the
module will send back the latest actual value data stored in the MDP, these values will be periodically read
by the module from the MDP relay.
c) FORCE SINGLE COIL: FUNCTION CODE 05
Modbus description: Forces a single coil (OX reference) to either ON or OFF. When broadcast, the function
forces the same coil reference in all attached slaves.
MDP function to force: Breaker trip and breaker close.
•
QUERY: The query message specifies the coil reference to be forced. Coils are addressed starting at zero:
coil 1 is addressed as 0. The request ON/OFF state is specified by a constant in the query data field. A
value of FF00 hex requests the coil to be ON. A value of 0000 requests it to be OFF. All other values are
illegal and will not affect the coil.
•
RESPONSE: The normal response is an echo of the query, returned after the coil state has been forced.
7
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2
Courtesy of NationalSwitchgear.com
MDP Digital Time Overcurrent Relay
GEK-100682D
GE Power Management
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