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CHAPTER 10: MULTI DROP CONNECTION
One MODBUS TCP Interface can control more than one power supply. A maximum of 31 units
can be connected via RS485 interface to a power supply with the installed MODBUS TCP option.
The power supply connected to a PC via the Ethernet cable must be configured to MODBUS TCP (OPT)
communication interface, the other units must be configured to RS485 interface. Each unit must have a
unique address, ranging from 0 to 31.
MODBUS TCP module automatically receives the address of the unit
into which it is installed. For RS485 interface set Baud rate to “115200" bps and Communication Language to
"SCPI". Refer to USER MANUAL (IA761-04
-02_), Multi Power Supply Connection (Daisy-Chain)
for instructions regarding system setup.
10.1
Selecting a Single Power Supply in a Multi Drop Chain
All MODBUS TCP commands may be sent to any one of the power supplies in RS485 chain by sending the
INSTrument:NSELect <NR1> command (register 71). All commands and queries will then apply only to the
selected power supply, until a new INSTrument:NSELect <NR1> command
(register 71) is sent.
At power-up, the MODBUS TCP master power supply is automatically selected.
After sending INSTrument:NSELect <NR1> command (register 71), it is recommended to verify the command
by sending INSTrument:NSELect? (read register 7
1), to make sure the following commands are not sent to
the wrong power supply.
10.2
Power Supply Configuration
To communicate over the MODBUS TCP interface, power supply has to be configured to MODBUS TCP. If
MODBUS TCP option is installed, by default, power supply is pre-configured to the MODBUS TCP
communication.
If, for any reason, MODBUS TCP communication is not selected, navigate to communication menu and select
OPT. Refer to USER MANUAL (IA761-04
-02_) for instructions to set the MODBUS TCP (OPT)
communication interface via the Front Panel or SYSTem:[COMMunicate]:INTerface <DSC> command to
select communication interface
by communication.
NOTE
Multi-User control is not allowed in Multi-Drop configuration (power supplies are connected by Daisy-Chain
RS485 connection).
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