Ebyte 4440-GPRS User Manual page 15

Wireless Data Transceiver
4.2 IO basic function
4.2.1 switch DO output
Read switch DO output

Function code: 01, Read coil state
Address range：00017(0x0010)~00020(0x0013)
Note: When the device relay is passively output, and the coil is not power on, the NC and COM of
the relay are normally closed, the NO and the COM are normally open, the value is 0; when the coil is
power on, the phenomenon is reversed, the relay NC and COM are disconnected, the NO and the
COM are closed, and the value is 1. The relay state can be queried by command.
For example:
When reading the 4-channel switch output state, assume that the return value is 03,
corresponding to the binary bit 0000 0011, the lower four bits represent the switch output state, which
in turn is DO4, DO3, DO2, DO1.
Modbus RTU protocol read switch output:
01
Device
Send
ModBus
address
01
Receive
Device ModBus
address
Modbus TCP protocol read switch output:
00 01
Transmi
Send
ssion Protocol
identifie identifier
r
00 01
Transmi
Receive ssion Protocol
identifie identifier
r
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01 00 10
Function
Start address
code
01
Function
Bytes returned
code
00 00 00 06 01
Unit
Length identifie
r
00 00 00 04 01
Unit
Length identifie
r
00 04
Read number of
switch quantity
01 03
Switch Output
Value
01 00 10
Functi
on Start address
code
01 01
Functi
on Bytes returned
code
E850-DTU(4440-GPRS) datasheet
3C 0C
CRC code
11 89
CRC code
00 04
Read number
of switch
quantity
03
Switch Output
Value
15