3-20
3
3.7
MODBUS COMMANDS
The following commands are used to Control Modbus slave devices. These
Modbus Commands should not be mixed or concatenated with IEEE-488.2 or
SCPI commands. Commands marked with an asterisk are new in the 48x9A
series interfaces and are not available in the older 48x9 interfaces.
TABLE 3-5 MODBUS COMMANDS
Syntax
Meaning
C addr
Modbus Address Command. Sets Modbus slave device
address for subsequent commands. Value for
addr
is 1
to 255. Default setting is 1.
RC[?] reg, ncoil *
Read Coil Status Command (code 0x01). Reads the
status of coils in a remote device. User specifies start-
ing coil address in register
reg
and number of coils to
be read
ncoil
. The [?] is an optional symbol for smart
programs.
(4)
Values for
reg
are 0 to 65535. Values for
ncoil
are 1 to 2000. Responses are returned as a packed
binary value with 1-bit per coil, 8 coils per byte. 1 =
ON.
RI[?] reg, ninp *
Read Discrete Inputs Command (code 0x02). Reads
discrete inputs. User specifies starting address in
register
reg
and number of inputs to be read
ninp
. The
[?] is an optional symbol for smart programs.
(4)
Values
for
reg
are 0 to 65535. Values for
ninp
are 1 to 2000.
Responses are returned as a packed binary value with
8 inputs per byte. 1 = ON.
R[?] reg, num
Read Register Command (code 0x03). Reads one or
multiple Modbus device registers. User specifies start-
ing register
reg
and number of registers to be read
num
.
The [?] is an optional symbol for smart programs.
(4)
Values for
reg
are 0 to 65535. Values for
num
are 1 to
64. Responses are returned as signed 16-bit decimal or
HEX values , +32767 to -32767, separated by commas.
Output format selected with the Format command.
i.e.
R? 0,1 reads Watlow Model Number. Response is 5270
for Watlow Model F4
R? 0,3 reads three successive registers. Response is
5270, 0, 123 for the Watlow F4 Controller.
Summary of Contents for 4809A
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