BECKHOFF EtherCAT Technology Section I - Manual (Page 104)

Watchdogs
I-84 Slave Controller – Technology
13 Watchdogs
The ESCs support up to two internal watchdogs (WD), a Process Data watchdog used for monitoring
process data accesses, and a PDI watchdog monitoring PDI activity.
The timeout for both watchdogs can be configured individually, but they share a single Watchdog
Divider (WD_DIV, register 0x0400:0x0401). The watchdog timeout is calculated from the Watchdog
Divider settings multiplied with the Watchdog Time settings for PDI (WD_PDI, register 0x0410:0x0411)
or Process Data (WD_PD, register 0x0420:0x0421). Base time unit is 40 ns. The Watchdog timeout
jitters, the jitter depends on the Watchdog Divider settings. I.e., selecting smaller Watchdog Divider
settings results in smaller jitter.
The following equations are used for a quick estimation of the watchdog timeout (they are not exact in
terms of nanoseconds):
t
WD_Div
= (WD_DIV + 2) * 40ns
t
WD_PDI
= [t
WD_Div
* WD_PDI ; t
WD_Div
* WD_PDI + t
WD_Div
]
t
WD_PD
= [t
WD_Div
* WD_PD ; t
WD_Div
* WD_PD + t
WD_Div
]
Registers used for Watchdogs are described in Table 49:
Table 49: Registers for Watchdogs
Register Address Name Description
0x0110[1] ESC DL Status Status PDI Watchdog
0x0400:0x0401 Watchdog Divider Watchdog Divider (WD_DIV)
0x0410:0x0411 Watchdog Time PDI Watchdog Time PDI (WD_PDI)
0x0420:0x0421 Watchdog Time Process Data Watchdog Time Process Data (WD_PD)
0x0440:0x0441 Watchdog Status Process Data Status Process Data Watchdog
0x0442 Watchdog Counter Process Data
Watchdog expiration counter Process
Data
0x0443 Watchdog Counter PDI Watchdog expiration counter PDI
0x0804 +N*8 SyncManager Control Watchdog trigger enable
NOTE: Some of these registers are not available in specific ESCs. Refer to Section II for details.
13.1 Process Data Watchdog
The Process Data watchdog is rewound (triggered) by a write access to a SyncManager buffer area if
the SyncManager is configured to generate a watchdog trigger signal (SyncManager Control register
0x0804[6] for SyncManager 0, etc.). The watchdog trigger signal is generated after the buffer was
completely and successfully written (similar to the Interrupt Write of a SyncManager).
The Process Data watchdog can be disabled by setting the Process Data Watchdog Time to 0.
A timeout of the Process Data watchdog has these consequences:

Watchdog Status register for Process Data (0x0440[0]) reflects the watchdog status.

The Digital I/O PDI takes back digital output data, either by not driving the signals anymore or by
driving them low (ESC and configuration dependent).

The Watchdog Counter Process Data (0x0442) is incremented.
13.2 PDI Watchdog
The PDI watchdog is rewound (triggered) by any correct read or write access by the PDI. The PDI
watchdog can be disabled by setting the PDI Watchdog Time to 0.
A timeout of the PDI watchdog has these consequences:

ESC DL Status register (0x0110[1]) reflects the watchdog status. This can be mapped to the
ECAT Interrupt to inform the master.

The Watchdog Counter PDI (0x0443) is incremented.
NOTE: The Digital I/O PDI only triggers the PDI watchdog upon input events.