Heartbeat

Hello,

I am working on a hydraulic control system based on MD5 and MC43. The main control logic runs in MC43, while MD5 handles non-safety UI functions.

To ensure safe operation, I implemented a simple heartbeat between MD5 and MC43:

Setup:

• Heartbeat: digital signal toggling TRUE/FALSE every ~100 ms in MD5
• Transmitted via J1939 to MC43
• MC43 monitors time since last change
• System cycle time: 50 ms
• Safety action: if no change for >500 ms, MC43 disables outputs
• Logging is active on both MD5 and MC43

Problem:

The heartbeat signal is periodically lost or appears frozen for short periods (typically 100–3000 ms, sometimes longer), triggering safety shutdowns.

Test setup (minimal system):

• Only MD5 and MC43 connected
• 30 cm CAN cable
• Two 120Ω termination resistors at both ends
• No other CAN nodes
• Minimal application: only one J1939 message + heartbeat logic
• No HMI logic or additional communication

The issue still occurs in this simplified configuration.

Tests performed:

• Different CAN speeds (including 250k / 500k/1000)
• J1939 and generic CAN communication modes
• Same behavior observed across configurations
• No communication errors reported in internal Parker logs

Question:

Has anyone observed similar intermittent J1939 communication drops between MD5 and MC43 under otherwise stable conditions?