Allen-Bradley DeviceNet 1761-NET-DNI, User Manual, Page: 78 / 101

1761-6.5
7-4 Application Examples
DNI - MicroLogix Heartbeat Logic
DNI I-O.RSS Ladder 2 - Main Program
Note: Rung 9 in this example resets (0) all outputs to off if
communications are lost. If you prefer your application to have the
controller maintain the outputs in their last state, remove this rung.
Or, if you want additional logic to control your outputs, remove this
rung and program the outputs as your application requirements
warrant.
0000
S:0
8
0001
N7:95
7
OSR
B3:31
15
B3:31
14
0002
N7:95
7
OSR
B3:31
13
B3:31
12
0003
B3:31
14
B3:31
12
RES
T4:39
0004
EN
DN
TON
Timer On Delay
Timer
T4:39
Time Base 0.01
Preset 350<
Accum 22<
TON
This rung sets status file bit S2:0/8. When this bit is set, it allows a program written for a 32-point
MicroLogix 1000 controller to run without an I/O mismatch error on a 10, 16, or 25-point controller.
Extend I/O Configuration
DNI Heartbeat Pulse On Detected Off-to-On Memory Heartbeat Bit from DNI
This rung detects an off-to-on transition of bit N7:95/7. Bit N7:95/7 is the communication’s Heartbeat that is received
from the DNI.
DNI Heartbeat Pulse Off Detected On-to-Off Memory Heartbeat Bit from DNI
This rung detects an on-to-off transition of bit N7:95/7. Bit N7:95/7 is the communication’s Heartbeat that is
received from the DNI.
DNI Communications Watchdog
DNI Heartbeat Pulse On Detected
This rung resets the communications watchdog whenever the DNI Heartbeat changes state (off-to-on or on-to-off).
DNI Heartbeat
Pulse Off Detected
Timer 39 is the communications watchdog for DNI/MicroLogix communications. If this timer ever “times out”, the
outputs directly controlled by the MicroLogix turn off. This timer is constantly being reset by the status of bit N7:95/7
(toggle on, toggle off). Bit N7:95/7 is controlled by communications received from the DNI. The amount of time (preset)
the timer should be set to is dependent on the DF1 Heartbeat, Data Scan Delay, and the baud rate of the RS-232 port.
Using this logic with a Series D MicroLogix 1000 controller, set T4:39 to a preset value of 350 ms. If communications
are lost with the DNI, the MicroLogix 1000 turns off its outputs after 350 ms.