Slave device
Physical memory
Logical address space
FMMU
Out
put
Input
Figure 11.64:
The FMMU mapping logical and physical memory addresses
● SyncManager
A SyncManager controls the access to the slave´s physical memory. Each
SyncManager channel defines a consistent area of physical memory. To
use the slave´s physical memory in a coordinated fashion (e.g. to handle
concurrent access of objects stored in physical memory), a SyncManager
provides two ways of coordinated communication:
1
Buffered mode, which allows consistent reading and writing in both
directions. This mode is used for cyclic Process Data exchange.
2
Mailbox mode, which enables interlocked communication. One entity
fills in the data and the memory area is locked until the other entity reads
out the data. This mode is used for on
-
demand data exchange.
● Distributed Clocks
For synchronization a distributed clocks (DC) mechanism can be used,
which leads to very low jitter, significantly less than 1 µs, even if the
communication cycle jitters, which is equivalent to the IEEE 1588 Precision
Time Protocol standard (PTP).
The system clock is specified as a 64 bit counter with a base unit of 1
nanosecond starting at January 1, 2000, 0:00.
For a detailed description of DC and its capabilities see [ETG.1000
-
4].
11.10.5
Application Layer
The EtherCAT
®
application layer provides user programs with means to access
the underlying EtherCAT
®
field bus environment.
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