| ??? 01/27/06 08:35 Read: times |
#108482 - Exception Responding to: ???'s previous message |
Dear Abhishek,
Abhishek Singh said:
if you have a '0' on the latch and you want a input from external world (thats a ports job, not reading back what is inside the micro i.e. latch values) you have to put a one in to it and this action is called "configuring a pin as INPUT".
In case you indicated (port pins are '0's), writing '1's into the latch causes exactly OUTPUT behaviour of a port: all pins activate strong pull-up for 2 OSC cycles and emit '1's with possible very high current for this time. By other words, if external peripheral provides low level to these pins at this time then short-circuit happens. Indeed, this is only for two OSC cycles but remember that 8051 may work at low frequences so this period may be long enough to destroy hardware. By the way, looking at this picture: 
could you say that "writting '1' to the P1.0 sets it to input mode"? For me, with both '0' and '1' the pin is still output. Regards, Oleg |
