Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, PRIOR to Firmware rev. 3.0 - Manual (Page 89)

Publication 1404-UM001D-EN-E - October 2004
Communications 4-29
For function code 03, 04 and 16, if any undefined starting address is
sent to the Powermonitor 3000, exception code 2 will be returned and
error code 6 will occur. If the starting addresses other than the first
Modbus address of the data tables are sent to the slave with function
code 16, this error code will also occur.
For function codes 03 and 04, the starting address may be any address
within the data table. However, for floating point data tables, one
element occupies two Modbus addresses. Therefore, only odd
Modbus address are allowed when accessing floating point data table.
If the starting address is even, error code 7 will occur.
Table A.53 Controller Command is the only one table that has write
only attribute. If the user tries to use function code 03 to read this
table, error code 8 will occur and a 02 exception response packet will
be returned.
Auto-sense protocol selection
The primary purpose for auto-sense is to permit configuration using
RSPower32 on a point-to-point RS-485 connection by disabling the
Modbus master station and enabling a DF-1 polling master in RSLinx.
The port switches back to the Modbus protocol when it detects
incoming Modbus data packets. Simultaneous use of Modbus and
DF-1 master stations on the same network is not permitted or
supported.
When auto-sense is selected, when a port configured as Modbus
detects incoming DF-1 half-duplex data packets, it automatically
switches to the DF-1 half-duplex protocol at the same baud rate and
other communications parameters. The port may return a
communications error to the first non-selected packet and then switch
protocols. The client should be set up to retry communications if it
receives an error.