Post by thread:[PIC]: Can a PIC switch fast enough to harm memory

Some memory chips have warnings about fast bus transceivers causing undershooting at inputs to the memory chips. This apparently is due to inductance in the PCB trace, and a lack of clamping diodes on the transceivers. Is it safe to assume that transistions on PIC output pins are slow enough that this isnt a problem? In other words, is it safe to directly connect PIC outputs to RAM or FLASH chips of the same voltage? -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Nicholas Irias wrote... >Some memory chips have warnings about fast bus transceivers causing >undershooting at inputs to the memory chips. This apparently is due to >inductance in the PCB trace, and a lack of clamping diodes on the >transceivers. > >Is it safe to assume that transistions on PIC output pins are slow >enough that this isnt a problem? In other words, is it safe to directly >connect PIC outputs to RAM or FLASH chips of the same voltage? Checking the data sheet for the PIC16F877, Microchip lists output port pin rise and fall times of 10 nanoseconds minimum and 40 nanoseconds maximum. For the PIC18C452, it's 10 to 25 ns. Those are pretty slow rise and fall times, and with these kinds of numbers I wouldn't expect to have significant undershoot/overshoot problems. If you really want to make sure there aren't any problems you can put resistors in the lines going between the PIC and the memories, at either end. Fifty ohms should do. Hope this helps... Dave -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics