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Allen-Bradley MicroLogix 1100 Instruction Set Reference Manual

Allen-Bradley MicroLogix 1100
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Publication 1763-RM001B-EN-P - April 2007
372 Communications Instructions
Input registers and holding registers are addressed at the word level.
Input registers are generally used for internally storing input values. They
are read-only. Holding registers are general purpose and can be both read
and written.
The most significant digit of the address is considered a prefix, and does
not get entered into the MB Data Address field when configuring the
message instruction.
When the message is sent, the address is decremented by 1 and converted
into a 4-character hex number to be transmitted via the network (with a
range of 0-FFFFh); the slave increments the address by 1, and selects the
appropriate memory group based on the Modbus function.
Local/Slave Node Address
This is the destination device's node number if the devices are on a
DH-485, DeviceNet (using 1761-NET-DNI), DF1, or Modbus network.
TIP
Modbus protocol may not be consistently implemented
in all devices. The Modbus specification calls for the
addressing range to start at 1; however, some devices
start addressing at 0.
The Modbus Data Address in the Message Setup Screen
may need to be incremented by one to properly access a
Modbus slave’s memory, depending on that slave’s
implementation of memory addressing.
TIP
To initiate a broadcast message on a DH-485, DF1
Half-Duplex, or DF1 Radio Modem network, set the local
node address to -1.
To initiate a broadcast message on a Modbus network,
set the slave node address to 0. Do not initiate more than
one Modbus broadcast message at a time. When
sequentially triggering multiple Modbus broadcast
messages, insert at least 10 msec. delay in between each
message.
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Allen-Bradley MicroLogix 1100 Specifications

General IconGeneral
Processor32-bit
Programming SoftwareRSLogix 500
MountingDIN rail or panel mount
Power Supply24V DC
TypeCompact PLC
Digital Inputs12
Digital Outputs8
Analog Inputs4 (depending on model)
Analog OutputsOptional with expansion module
Programming LanguageLadder Logic
Operating Temperature0 to 55 °C (32 to 131 °F)
SeriesMicroLogix

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