
Date Code 980420
Operation and Network Configuration
3-1
SEL-2711 Instruction Manual
SECTION 3: OPERATION AND NETWORK CONFIGURATION
I
NTRODUCTION
This section describes the operation of the SEL-2711, including how to access data, LED
interpretation, self-tests, device configuration, and network configuration. This section is intended
primarily as a reference section. See
Section 4: Operation Within SEL-2030
for information on
installation and initial checkout.
D
ATA
A
CCESS
The SEL-2711 supports eight data slave paths (addresses 1 - 8) for access of data using Modbus
Plus. Thus, in a system with multiple hosts, each can access a different slave path, preventing
contention over access to the SEL-2711. The SEL-2711 also supports eight data master paths
which it uses to issue control commands to other nodes.
Data can be read from the SEL-2711 as holding registers using the Modbus Read Holding Register
function code (3). Using this function code, up to 125 consecutive registers can be read at once.
To read more than 125 registers requires multiple requests. See
Appendix C: Modbus Plus
Message Example
for an example of one of these messages.
Most devices that poll the SEL-2711 reference holding registers as starting at address 40001 (4x
reference). Some devices may reference using an offset value starting at 1, so you must subtract
40000 from the 4x reference address to determine the address to use. Other devices may reference
the data using a Modbus offset value which starts at 0 (this corresponds to how the holding register
address is actually transmitted on the network), so you must subtract 40001 from the 4x reference
address to determine the address to use.
From many Modicon PLCs, holding registers are read using a MSTR ladder logic function. The
MSTR instruction references holding register offset values, not absolute 4x addresses. Therefore,
you must subtract 40000 from the 4x addresses indicated in this manual.
Data can also be read from the SEL-2711 as input registers using the Modbus Read Input Register
function code (4). Using this function code, up to 125 consecutive registers can be read at once.
To read more requires multiple accesses. Input registers start at address 30001 (3x reference).
Similar to holding registers, it may be necessary to subtract 30000 or 30001 from the absolute 3x
address to determine the address to use within your system.
The state of coils can be read from the SEL-2711 using the Modbus Read Coil function code (1).
Using this function code, up to 2000 coils can be read at once. Coil addresses start at address 1
(0x reference). Most systems will use the coil address directly, but those that use a 0-based
reference will require you to subtract 1 one from the specified coil address.
In addition to reading data, it is possible to control some coils using the Modbus Force Single Coil
function code (5). You can set a coil ON or OFF, which corresponds to setting or clearing a
control point in the host system. Coil addressing for control is the same as for reading, as
described in the previous paragraph.