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Section 3
Vendor-specific implementation
3.3.3.2
3.3.3.3
3.3.4
18
not result in any Modbus exception response. The value in these bits or registers is always
zero.
One bit data mapping
All one bit data in the IED is readable either from the 0X or 1X memory area. The Modbus
bit point addresses are similar regardless of the memory area.One bit data is also available
in 4X register memory area as bit packed 16 bit registers. The bit locations follow a pattern
similar to the 0X and 1X locations.
Data in control direction
IED controls, set points and acknowledgements are mapped to Modbus 0X data (coils).
Coils can only be operated one by one.
Currently the ANSI implementation of controls via the Modbus protocol are restricted to
the 4X registers map.
Some control bits are packed bits in the 4X control register structures. The 4X control
structure contains a password which has to be given before starting control operations.
Digital input data
Indication signals related to protection applications often change rapidly. Thus, the
Modbus master might not be able to detect all changes.
Momentary- and momentary change detect bits
In this IED, indications are presented as two adjacent Modbus bits in the Modbus memory
map. The two bits represent the momentary position and the momentary change detect
state of the indication.
MOM
MCD
Figure 2:
Change detection bit
If the momentary value of an indication bit has changed two times or more since the master
last read it, the MCD bit is set to one. When the MCD bit has been read, it is reset to zero.
Since indications usually are 1-active, it is easy to detect an indication activation by
combining the MOM and MCD bits using a logical OR operation (MOM+MCD). The
1MAC052634-MB D
615/620 series ANSI
Communication Protocol Manual
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