Rockwell Automation 1761-NET-DNI DeviceNet Interface (DNI) - Manual (Page 43)

Publication 1761-UM005B-EN-P - October 2006
DNI Configuration Parameters and Programming Notes 43
DF1 Heartbeat
The DF1 data heartbeat is used to detect a valid communications path
between the controller and the DNI and also to detect if the
connected controller is scanning its ladder logic.
The heartbeat is enabled when:
• DNI Series A: Data Enable is enabled and DNI Mode is
operational
• DNI Series B: I/O Scan Enable is enabled
The heartbeat consists of a bit in the first byte (byte 0, bit 7) of the
data packet that is exchanged with the controller. The DNI sets this bit
in the output data being sent to the controller. The user must move
this bit, using ladder logic, to the corresponding bit position in the
input data area where the bit is then read from the controller by the
DNI.
At the heartbeat rate, once the DNI sees the bit return in its correct
state, it toggles the bit to the opposite state and sends it back to the
controller (this is a round robin process). If the bit state does not
change, it is detected as a communication/controller error and
reported to the DNI master as a zero-length packet. Refer to your
scanner or master controller documentation to determine how this is
detected in the master logic.
This bit should also be monitored by the controller attached to the
DNI, and if the bit does not change in the output image at the
heartbeat rate, it can be used within the controller to detect a problem
with the DNI/DeviceNet Master.
DF1 Heartbeat Parameter Definition
Parameter
Type Parameter Number Description Range Default
Value
Series A Series B
I/O 12 13 DF1 Heartbeat Series A: 2…10
Series B: 1…10 2