Timing Of The Data Transmission - Balluff BIS U-4A7-082-01C-07-S4 Betriebsanleitung

BIS U-4A7-082- _1C-07-S4
Industrial RFID system - Read/write head
8
System integration (continued)
8.10

Timing of the data transmission

The following figure shows the chronological sequence of
IO-Link communication. Input and output buffers are
always exchanged alternately. As soon as current data is
present in one of the buffers, it is exchanged with the next
starting in or out data cycle. Here, the problem arises that
the transmission times can fluctuate greatly. If data is
updated shortly before the start of the corresponding
exchange cycle, the transfer takes only slightly more than
1 x cycle time. However, if the data is updated shortly after
the start of an exchange cycle, it takes at most 2 x cycle
time.
The chronological sequence for processing a command is
shown on the next page, using the example of a read
assignment of 9...16 bytes (2 x input buffer for read data).
Timing between higher-level bus system, IO-Link
transmission and transmission time
Assumption:
– Cycle time of bus system 4 ms (t1)
– Cycle time of IO-Link 8 ms (t2)
– Data transmission from the controller to the IO-Link
device
Best case:
New data
4 ms
Bus system
8 ms
IO-Link
Worst case:
New data
4 ms
Bus system
8 ms
IO-Link
An offset occurs between the bus system and IO-Link,
since the bus system and IO-Link operate independently of
each other (not synchronously).
76 english
IN OUT IN OUT
Transfer time ≈ t + 1/2 t
1 2
IN OUT IN OUT IN
Transfer time ≈ t + 1.5 t
1 2
OUT