snap ethernet-based i/o units protocols and programming guide

CHAPTER 5: ADVANCED MODBUS PROGRAMMING
4. To convert a brain memory map address to a Modbus Unit ID and Register Address, type
the last eight digits of the brain’s memory map address in the MemMap Address field.
Make sure there are no spaces in the address (for example, type F0300020).
5. Click the right-arrow button .
The equivalent Modbus address appears. NOTE: The Modbus numbers are decimal.
Example: Reading a Memory Map Address
For example, suppose you want to read the status of Scratch Pad bits. You can determine the
memory map address in one of two ways:
Use the ioManager Inspect window to find the address you want and copy it.
Look in Appendix A, find Scratch Pad addresses (page 129), and locate the address for the
current state of Scratch Pad bits.
Either way, you determine that the memory map address is F0D80000. Using ioManager, you
convert the MemMap address F0D80000 to a Unit ID of 110 and a Register Number of 1.
Example: Writing to a Memory Map Address
As another example, suppose you want to send a powerup clear (PUC) to the brain. This operation
code is in the Status Write area of the brain’s memory map address. To determine the address
and the data to write to send a PUC, check the Status Write area in Appendix A (page 107).
From the appendix, you determine that the memory map address for an operation code is
F0380000, and the specific data you must write to send a PUC is 0x00000001. Using the Modbus
conversion page, you find that address F0380000 equals a Unit ID of 30 and a Register Number
of 1.
SNAP Ethernet-Based I/O Units Protocols and Programming Guide 101