I am using a 87C520 from Maxim (Dallas Semi). I have setup two Interrupts one is timer2 and one is serial port. Timer2 simply increments 5 variables and gets out time to execute is about 5MS Interrupt is set 50MS time frame. Now the serial is set with highest priority it is used to talk to other devices via MODBUS protocol. Set to 9600,8,N,1
Here is my issue when I run my program on the Emulator it runs perfect and it works great we can talk to all other devices without any issues Day in day out. But when I run the program on the actual unit without the emulator it runs anywhere between 40 - 60 times then it looks up and the Hardware watchdog will reset the board. Watchdog is set to 8 Seconds.
Here is my question has seen this type of problem with two Interrupts. I thought that the problem was that the Interrupts fighting each other so I made it that if one interrupts is active the other would be disabled but no luck. Any ideas?

Many thanks
Ray B