Data In Control Direction; Digital Input Data - ABB Relion 620 Series Protocol Manual

Section 3
Vendor-specific implementation
3.4.3.4
3.4.4
24
This is easier to understand when the address numbers are expressed in the
hexadecimal format: 2893 = 0xB4D, where the register 180 = 0xB4 and bit 13 = 0xD.

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.
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

As the indication signals related to protection applications often change rapidly, the
Modbus master may not detect all the changes.
Momentary position and momentary change detection bits
In this IED, indications are shown as two adjacent Modbus bits in the Modbus
memory map. The two bits represent the momentary position and the momentary
change detection state of the indication.
MOM
MCD
LATCH
A070894 V3 EN
Figure 3: 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 the 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 momentary position bit and the MCD bit of a certain
indication point always occur as pairs in the Modbus memory map. The momentary
bit is always located on an even bit address. MCD bit on the next odd bit address.
1MRS757645 B
620 series
Communication Protocol Manual