| ??? 01/27/06 00:48 Modified: 01/27/06 01:19 Read: times |
#108452 - Who is babbling? Responding to: ???'s previous message |
Abhishek said:
These ports are quasi bidirectional so they are always in output mode. If you connect these pins to some digital inputs those inputs will follow the voltages on the pins, which is echo of the latch values. So you dont have to initialize a port as output port. But if yo want to let the other digital outputs drive it you must initialize latch values to all '1's. Abhishek is totally right! By the way, the "Bible" itself supports the idea of "input mode" and "output mode", when they write: "Each I/O line can be independently used as an input or an output. ... To be used as an input, the port bit latch must contain a 1, which turns off the output driver FET." "Because Port1, 2 and 3 have fixed internal pull-ups, they are sometimes called "quasi-bidirectional" port. When configured as inputs they pull high and will source current when externally pulled low." "All the port latches in the 80C51 have 1s written to them by the reset function. If a 0 is subsequently written to a port latch, it can be reconfigured as an input by writing a 1 to it." So, what's so wrong to distinguish between "input mode" and "output mode"? If this is misleading, then the phrase "quasi-bidirectional" also is. It all depends on what you actually mean by these phrases. By the way, you should think about your relationship to the other forum members. I would never ask you to stop "babbling"! Kai |
