12.2.2. To Set the RS-485 Address:
In addition to the supply’s IP address, the multi-drop requires setting an RS-485 address. It is viewed on
the front panel of the power supply by setting it to local mode (see section 3.2.1) and pressing and holding
the REM/LOC button. The address may then be changed by turning the voltage encoder.
The default RS-485 address is 6. It may be set to any value from 0 to 30. The RS-485 address is not related
to the IP address. However, it is required that no other power supply on the multi-drop chain have the
same RS-485 address.
12.3. Connect and Configure the RS-485 Supplies
The RS-485 linked power supplies are called the Slave supplies. They may be individually commanded and
queried using the LAN port on the Master supply.
The RS-485 power supplies must be Multi-drop enabled
12.3.1. To Verify the Multi-drop is Enabled:
A. The power supply product label may have “-MD” in the model description.
B. Or try running the multi-drop chain. Open the LAN web page. On the DC Power page, click the “Refresh
List” control (see section 6.5.1). The addresses of all the multi-drop enabled RS-485 supplies will be
shown in the list
C. Or use the RS-232/485 port with a communication program such as HyperTerminal to send the “MDAV?”
query. if the response is “1”, the multi-drop is enabled in the supply. Refer to the Technical Manual for
details on using the RS-232/485 port.
12.3.2. To Set Up an RS-485 Chain:
A. If the supply has the LAN option, disable the option by sliding the LAN enable switch to DOWN. See
section 3.3.1 and Figure 3.
B. Set the supply into RS-485 mode by setting rear-panel SW1 bit 6 to UP.
C. Connect the RS-485 Link Cables from the master’s J3-OUT to the slave’s J3-IN.
D. Power-up the supplies.
E. Set the supply’s RS-485 address as described in section 12.2.2.
F. While you are setting the address, it is required to also set the BAUD rate to 19.2K by turning the current
encoder.
12.3.3. Optional RS-485 Terminator
For very long RS-485 cable distances, or if many supplies are chained together, a signal terminator may
added to improve signal integrity. The terminator is plugged into the J3-OUT of the last supply in the chain
(see diagram above). To make a terminator:
A. Crimp a short cable to a RJ-45 connector (or just use the end of a LAN cable)
B. Use two ! watt resistors, recommended value is 120 ohms, and solder them:
from pin-3 to pin-6 (TXD+ to TXD–)
from pin-4 to pin-5 (RXD+ to RXD–)
C. Although the RS-485 bus should not be at hazardous voltages, insulate the terminator properly for your
application
12.4. Multi-drop Programming Using SCPI Commands
12.4.1. Selecting One Power Supply in a Multi-drop Chain
All the SCPI commands in section 11 may be sent to any one of the supplies in an RS-485 chain by first
sending the
INST:SEL address command. All commands and queries will then apply only to the selected
supply, until a new
INST:SEL is sent.
At power-up, the LAN master supply is automatically the one selected.
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