INM 725B Rev 21
89
13 .4 .6 Modbus Slave – Standard Communications
Function Descriptions
This section describes the process of reading from and writing data to a RTK 725B slave
annunciator
13 .4 .7 Read Coil Status – Function 01 – Request
Register Address
This is used to address the “start” channel to be read for example the first channel in the
system “channel 1” would be register address 00 00
To read the port register coil value the port offset is used to define the start address.
To read the current contact or alarm status then the start address is defined by the contact
offset.
To read the input status read coils 0- 255
To read the alarm status read coils 300- 555
Number of Registers
This represents the number of coils, the user wishes to read. This can be 1-255 coils.
13 .4 .8 Read Coil Status – Function 01 – Response
Byte Count
This represents the number of bytes sent
Data
For the port register this will the value stored in the address requested. With Contact status
this represents the status of the requested coil for type of status requested.
Input
0 = Input Normal
1 = Input Abnormal
Alarm
0 = Alarm Normal
1 = Channel in alarm
Typical Example of Message Format
To read all of the inputs available on a 100 way annunciator with a node address of 5 using the
following message format
RTU
ADDRESS
FUNCTION
REGISTER ADDRESS
No. of REGISTERS
ERROR CHECK
05
01
00 00
00 64
3C 65
ASCII
:
ADDRESS
FUNCTION
REGISTER
ADDRESS
No. of
Registers
ERROR
CHECK
CR
LF
3A
30 35
30 31
30 30 30 30
30 30 36 34
39 36
0D
0A
