Exchanging I/O Data Over Profibus - Omron CJ Series Operation Manual

Data Type
Time of day
Time difference
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Exchanging I/O Data Over PROFIBUS

The cyclic refresh cycles of the CPU and the I/O data exchange cycles of the PROFIBUS network
are two asynchronous processes for which the CJ1W-PRM21 PROFIBUS Master Unit performs the
interface function.
 CPU Cyclic Refresh vs. PROFIBUS I/O Exchange Cycle
In general, all I/O data exchanged during a PROFIBUS I/O data exchange cycle must be exchanged
with the CPU as soon as possible after the end of each PROFIBUS DP I/O data exchange cycle is
signalled.
In order to transfer I/O data between the Unit and the CPU, the Unit has to request a transfer of I/O
data. The actual transfer of I/O data will then be performed during the next CPU cyclic refresh which
depends on the CPU user program.
 CPU Cyclic Refresh Rules
To avoid missing I/O data as much as possible the CJ1W-PRM21 uses the following rules for cyclic
refresh with the CPU.
• The PROFIBUS Master Unit estimates (based on the actual CPU cycle and the last cyclic refresh)
when a new cyclic refresh from the CPU can be expected and requests a refresh of I/O data
before the next refresh event.
• If the end of PROFIBUS DP I/O data exchange is signalled before the request based on the esti-
mation is issued, the PROFIBUS Master Unit will immediately request a cyclic refresh.
• If the end of PROFIBUS DP I/O data exchange is signalled after the request has been issued or
during the cyclic refresh, the PROFIBUS Master Unit will request a cyclic refresh as soon as the
requested cyclic refresh has been finished.
The implementation of these rules are illustrated in the figures below for two distinctive cases.
 PROFIBUS DP Cycle > CPU Cyclic Refresh
The figure below shows the effects of these rules for the case in which the PROFIBUS DP I/O data
exchange cycle > CPU cyclic refresh
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
Size [bytes] PROFIBUS DP
6 Supported.
Time of day format contains
time since midnight.
6 Supported.
Time difference format is the
same as Time of day format,
but contains a time differ-
ence.
5 Operation
NJ-series Controller Unit
Not Supported.
Time of day format is trans-
ferred to CPU memory as
string of words.
Not Supported.
Time difference format is
transferred to CPU memory
as string of words.
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