INTERNAL CONTROLLER MEMORY HELP

[mikeb]

DOES ANY ONE KNOW WHY A MICROCONTROLLER WOULD FAIL TO WRITE TO INTERNAL RAM ONCE THE CONTROLLER IS CONNECTED TO EXTERNAL DEVICES. THE PROBLEM IM HAVING IS GETTING INTERNAL RAM TO ACCEPT DATA WRITES WHEN THE CONTROLLER HAS EXTERNAL DEVICES CONNECTED TO ITS PORT OUTPUT AN INPUT PINS. I GUESS IM WONDERING IF THE OUTPUT PINS IF DRIVING TO MANY INPUTS WOULD CAUSE THE MICRCONTROLLER TO STOP WRITING TO INTERNAL EPROM. THEW CIRCUIT WORKS FINE OTHER THEN THE FACT THAT IT WONT WRITE TO INTERNAL MEMORY. MAYBE I NEED TO ADD A BUFFER IC TO THE OUTPUT PINS DRIVING THE EXTERNAL DEVICES, IF THEWRES ANY ONE WITH KNOWLEDGE ABOUT THE LOAD CAPACITY OF THE OUTPUT PINS OF A CONTROLLER ID APPRECIATE ANY ADVICE.

[bodgy]

Just a request, could you type in lower case? I don't know about others, but it is difficult (for me) to read your posts <p>Now you say that with nothing connected to the ports internal RAM writes work. Do you have an ICD or emulator that allows you to now this for certain?<p>One thing that may cause it to fail with external devices connected would be interrupts. If an external device fires an interrupt, then your uP will stop what it is doing and certainly for Pics, interrupts must be disabled whilst writing to EEPROM, and could cause RAM variables not to be updated correctly if the interrupt occurs as they are being actioned. If your uP doesn't have an automatic PUSH or POP instruction then you must save registers yourself.<p>There is the possibility that your external devices are drawing too much current and that could cause a power dip which would normally cause the controller to reset.<p>Another thing that would do this is if any chips are inadvertantly plugged in backwards, though you'd have soon found that one out.<p>Are any of these input/output pins dual purpose? IE one uP pin is both input or output and has two external devices connected to this pin. Does one pin drive more than one device?<p>Colin