Compact Mode Output Register Overview

In addition to the Input registers, each RMC module requires two 16-bit registers per axis to hold commands. The two command registers for each axis are processed each time the Synchronization Output register is changed.

When a Sensor DI/O module is installed, an additional two outputs words are reserved but are currently unused.

If Compact Mode with Sync is used (versus Compact Mode without Sync), one additional 16-bit register to hold the Synchronization Output register. See Using the PROFIBUS-DP Compact Mode for details on using this register and the differences between these two sub-modes.

The order of the output registers for an n-axis module with a Sensor DI/O running in Compact Mode with Sync is shown below. O represents the RMC’s output base address. If your module does not have a Sensor DI/O, drop the last two registers:

Register Number	Contents
O + 0	Synchronization Input
O + 1	Command – axis 0
O + 2	Data out – axis 0
O + 3	Command – axis 1
O + 4	Data out – axis 1
:	:
O + 2*n + 1	Command – axis n
O + 2*n + 2	Data out – axis n
O + 2*n + 3	Reserved by Sensor DI/O
O + 2*n + 4	Reserved by Sensor DI/O

The following chart shows the same for an RMC running in Compact Mode without Sync:

Register Number	Contents
O + 0	Synchronization Input
O + 1	Command – axis 0
O + 2	Data out – axis 0
O + 3	Command – axis 1
:	:
O + 2*n + 0	Command – axis n
O + 2*n + 1	Data out – axis n
O + 2*n + 2	Reserved by Sensor DI/O
O + 2*n + 3	Reserved by Sensor DI/O

PROFIBUS-DP has a much larger set of commands than the normal ASCII commands that can be used in the Command field, although ASCII commands are still available. For a complete description of using the Command and Data out registers, refer to Command Words for PROFIBUS-DP Compact Mode.