3.4.6.1
Control functions
Generally, output objects are controlled one at a time. The IED accepts only functions
05 (force single coil) and 15 (force multiple coils), when the 0X coils control structure
is used for control operation.
Only one control bit can be operated at a time when the 4X control structures are used.
Exception codes
Only a few exception code alternatives exist for the write coil and write register
requests in Modbus:
•
01 = illegal function
•
02 = illegal address
•
03 = illegal value
The exception code 03 is also returned if a command operation is rejected due to other
internal reasons. An additional internal reason code for the exception, can be found in
the SSR6 register after the command operation.
Internal control rejection reasons with coils may be, for example:
•
The client has no write authority.
•
The IED is in local or OFF state.
•
The control operation is already reserved by another client and thus blocked.
If a positive acknowledgement is returned, the control command has been initiated by
the IED.
3.4.6.2
Control operations through 4X register structures
The control outputs can be operated through the control structures in the 4X register
area. This means that the control output is also located as a bit within the value and bit
mask registers of the 4X control structure. Although usually less, there may be up to
eight control structures defined in the IED.
The control structure operations can be controlled with passwords. As a default, no
passwords exist for the structures. Any four character ASCII string can be used as a
password. The password string “****” with four asterisks, that is ASCII code 42,
indicates that a password is not used.
Table 15:
Single control structure
Location
Meaning
4x Reg N
Execute register
4x Reg N+1
Password register 1 high, two ASCII characters
4x Reg N+2
Password register 2 low, two ASCII characters
4x Reg N+3
Value register
4x Reg N+4
Bitmask register
1MRS757645 B
Section 3
Vendor-specific implementation
620 series
33
Communication Protocol Manual
