NOTE!
Coils and registers are addressed explicit with an off-set of
-1 in Modbus.
For example, Coil 33 is addressed as Coil 32.
7.10.2 Force/Write Single Coil (05 HEX)
Description
This function forces the coil to either ON or OFF. When
broadcast the function forces the same coil references in
all attached slaves.
Query
The query message specifies the coil 65 (parameter write
control) to be forced. Coil addresses start at zero, i.e., coil
65 is addressed as 64. Force Data = 00 00HEX (OFF) or FF
00HEX (ON).
Field Name
Example (HEX)
Slave Address
01 (Adjustable frequency drive
address)
Function
05 (write single coil)
Coil Address HI
00
Coil Address LO
40 (64 decimal) Coil 65
Force Data HI
FF
Force Data LO
00 (FF 00 = ON)
Error Check (CRC)
-
Table 7.23
Response
The normal response is an echo of the query, which is
returned after the coil state has been forced.
Field Name
Example (HEX)
Slave Address
01
Function
05
Force Data HI
FF
Force Data LO
00
Quantity of Coils HI
00
Quantity of Coils LO
01
Error Check (CRC)
-
Table 7.24
7.10.3 Force/Write Multiple Coils (0F HEX)
This function forces each coil in a sequence of coils to
either ON or OFF. When broadcast the function forces the
same coil references in all attached slaves.
The query message specifies the coils 17 to 32 (speed
setpoint) to be forced.
NOTE!
Coil addresses start at zero, i.e., coil 17 is addressed as 16.
Field Name
Example (HEX)
Slave Address
01 (Adjustable frequency drive
address)
Function
0F (write multiple coils)
Coil Address HI
00
Coil Address LO
10 (coil address 17)
Quantity of Coils HI
00
Quantity of Coils LO
10 (16 coils)
Byte Count
02
Force Data HI
(Coils 8-1)
20
Force Data LO
(Coils 10-9)
00 (ref. = 2000hex)
Error Check (CRC)
-
Table 7.25
Response
The normal response returns the slave address, function
code, starting address, and quantity of coils forced.
Field Name
Example (HEX)
Slave Address
01 (Adjustable frequency drive
address)
Function
0F (write multiple coils)
Coil Address HI
00
Coil Address LO
10 (coil address 17)
Quantity of Coils HI
00
Quantity of Coils LO
10 (16 coils)
Error Check (CRC)
-
Table 7.26
7.10.4 Read Holding Registers (03 HEX)
Description
This function reads the contents of holding registers in the
slave.
Query
The query message specifies the starting register and
quantity of registers to be read. Register addresses start at
zero, i.e., registers 1-4 are addressed as 0-3.
Example: Read
3-03 Maximum Reference
, register 03030.
RS-485 Installation and Set...
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®
HVAC Drive Design Guide
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