| ??? 02/01/06 14:38 Read: times |
#108892 - We talk about the "Bible"! Responding to: ???'s previous message |
Erik said:
the issue is not if someone can find references to some expression Erik, we talk about the "Bible"! And it's definitely stated there that the port can be configured as input. I quote the "Bible" now: "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 please accept the facts. The "Bible" is misleading and supports the (wrong) idea of 'modes', especially for people who also have a look into other datasheets (for instance P89LPC952), where philips people also talk about "configuration" but definitely mean the choosing of a "mode". Erik said:
the issue is that when explaining quasi-bidirectional everybody gets it in an instant, when babbleing about modes, just see the OP as to how confusing it is. Fact is, that this quasi-bidirectional stuff isn't easy at all. Only if you have understood the fine details of this topology, namely, that the outputs can be strong or weak, and that they are only strong for a very brief period of time, when, yes when you have configured the port as input, then it becomes clear, that you can drive the port by an external load, under certain circumstances. Kai |
