Omron PRT1-COM Operation Manual page 164

Remote I/O Communications Characteristics
8-1-4 Asynchronous / synchronous mode
154
N: Number of Special I/O Units (1 to 8)
The communication unit (PRT1-COM) can be programmed in either
asynchronous or synchronous mode.
For optimal performance use asynchronous mode. Use synchronous mode only
when:
1
/ * PROFIBUS-DP Cycle time ≤ MULTIPLE I/O Bus cycle time ≤
2
PROFIBUS-DP Cycle time
Both modes are explained with a timing diagram.
The following timing diagram shows an asynchronous transfer.
In this example, input data-3, rather than input data-2 is send with the next
PROFIBUS-DP data exchange cycle.
The following timing diagram shows a synchronous transfer.
For calculating MULTIPLE I/O Unit cycle time, see section 8-1-3.
Section 8-1