I would suggest to modify STARUP.A51 so that the test is executed at startup before the clearing of ram and passing control to main() or modify the Clear IDATA ram routine so that it will test the ram location and at the end write 0x00 to ram location.

Copy STARTUP.A51 to your project directory and modify it in assembly. If an error is detected enter and endless loop.

To do it from C, it is better to make an assembly module with the test function. Do it as Craig has suggested.

Franc