BECKHOFF EtherCAT Technology Section I - Manual (Page 66)

SyncManager
I-46 Slave Controller – Technology
Master µController
Slave writes data into mailbox
Master sends mailbox read
command
Mailbox read
Slave detects Repeat Request
(interrupt or polling)
Slave writes stored write data
into mailbox again
Maibox read data (WKC=1)
Timeout: Master detects
lost frame
Master toggles
Repeat Request bit
Toggle Repeat Request bit
Master polls Repeat Request
Acknowledge bit
Read Repeat Request Acknowledge bit
Repeat Request Acknowledge is set
Master sends mailbox read
command again
Mailbox read
Maibox read data A (WKC=1) Master receives mailbox read
data
ESC
Write data A
Interrupt
Write data A
Toggle Repeat
Request
Acknowledge
Read Event
Slave detects that mailbox was
read and stores write data for a
possible repeat request
Write data B
Slave writes next data into
mailbox
Slave toggles Repeat Request
Acknowledge bit
Communication proceeds with read data B
Figure 26: Handling of a Repeat Request with Read Mailbox
8.7 SyncManager Deactivation by the PDI
A SyncManager can be deactivated by the PDI to inform the master of local problems (typically used
in buffered mode only). The master can detect SyncManager deactivation by checking the Working
Counter, which is not incremented if a deactivated SyncManager buffer is accessed. If a SyncManager
is deactivated by the PDI (PDI Control register 0x7[0]=1), the state of the SyncManager is reset,
interrupts are cleared and the SyncManager has to be written first after re-activation. The entire
SyncManager buffer area is read/write protected while the SyncManager is deactivated by the PDI.