Local Messaging Examples - Allen-Bradley MicroLogix 1400 Instruction Manual

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Local Messaging
Examples
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.
Modbus protocol may not be consistently implemented in all devices. The
TIP
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.
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.
To initiate a broadcast message on a DH-485, DF1 Half-Duplex, or DF1
TIP
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.
Local/Remote
This variable defines the type of communications that is used. Always use
local when you need point-to-point communications via DF1 Full-Duplex
or network communications such as Ethernet/IP, DeviceNet (using
1761-NET-DNI), DF1 Half-Duplex, or DF1 Radio Modem. For DH-485, use
local if the target node is on the same DH-485 network as this controller,
or remote if the path to the target node goes through one or more
communication bridges.
Five examples of local messaging are shown in this section:
• 500CPU message type
Communications Instructions
Publication 1766-RM001A-EN-P - October 2008
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