Schweitzer Engineering Laboratories SEL-734, Instruction Manual

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F.9
Date Code 20090730 Instruction Manual SEL-734 Meter
Modbus RTU Communications Protocol
Modbus RTU Communications Protocol
The meter responses to errors in the query are shown in Table F.21 :
Modbus Password
Control and
Parameter
Modification
The SEL-734 parameters MID, TID, Password, and the User Map Registers
are settable via Modbus. Any settable parameter or reset that requires a valid
password write will time out 15 minutes after the last valid write to any of
these restricted registers.
Writing the password for access level change requires the 10h (preset multiple
register) command. Changing the password can be done one register at a time.
A device error is returned during settings save if the meter is disabled or
settings are being changed on another port. Device error is also returned for
attempts to write to settable values if the access level has not been changed.
To enable modification of the settable parameters, a valid Access Level
E (
EAC ) password must be written to the password registers through use of
function code 10h. Note that changing the password will change the password
for all ports.
Once you have written a valid password, change the values by using standard
single or multiple register writes (06h or 10h). Until a command is issued to
save or discard the settings, the value returned when reading the settable
parameter registers is a temporary copy.
To save the modified parameters, write a 0x0001 to the Save Settings register
of the Control I/O region. This is the only method that saves the changes.
To discard settings, either write a 0x0001 to the Discard Settings register of
the Control I/O region, write a 0x0001 to the Drop Access Level register of the
Control I/O region, or wait 15 minutes since last write for access level time-
out.
A successful response from the slave will have the following format:
1 byte Slave Address
1 byte Function Code (10h)
2 bytes Starting Address
2 bytes Number of Registers
2 bytes CRC-16
Table F.21 Responses to 10h Preset Multiple Registers Query Errors
Error Error Code Returned
Communication Counter
Increments
Illegal register to set Illegal Data Address (02h) Invalid Address Illegal
Write
Illegal number of
registers to set Illegal Data Value (03h) Illegal Register Illegal
Write
Incorrect number of bytes
in query data region Illegal Data Value (03h) Bad Packet Format Illegal
Write
Invalid register data value Illegal Data Value (03h) Illegal Write
Table F.20 10h Preset Multiple Registers Command (Sheet 2 of 2)
Bytes Field
Courtesy of NationalSwitchgear.com