Post by thread:[pic]: port buffer

16F628 with uart active I need to buffer writes to portB. Normal procedure is to write all values to a buffer and then move the entire buffer to the port. The port in question also services the uart ( send and receive ) Will i inject the wrong values into the uart by writing to the port or will the uart ignore my writes to the rx and tx bits (those bits will always be zero in the buffer )? John -- 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

If you check the diagrams on page 36 and 37 of DS40300B (the 16F62X data sheet), you'll see that there is a multiplexer (near the top) controlled by the "PORT/PERIPHERIAL" signal, that effectivily disables the output from the "Data Latch". So it would be "safe" to write any value to the PORTB register (the Data Latch), as far as I can see. Jan-Erik. John De Villiers wrote: > Will i inject the wrong values into the uart by writing to the port or > will the uart ignore my writes to the rx and tx bits (those bits will > always be zero in the buffer )? -- 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

John wrote: > I need to buffer writes to portB. Normal procedure is to write all > values to a buffer and then move the entire buffer to the port. > > The port in question also services the uart ( send and receive ) > > Will i inject the wrong values into the uart by writing to the port or > will the uart ignore my writes to the rx and tx bits (those bits will > always be zero in the buffer )? EVERY write to an I/O port (including BSF and BCF) actually writes all 8 bits. If the problem you fear actually existed, then you would not be able to safely use any of the other pins on the same port while the UART is active. The pin schematics in the datasheet will confirm that the UART completely bypasses the port register while it is active. Jason Harper -- 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

> > >Will i inject the wrong values into the uart by writing to the port or >will the uart ignore my writes to the rx and tx bits (those bits will >always be zero in the buffer )? > Normally, I won't be bothered to find out if it's going to be a problem or not. If I am going to use two pins as TX/RX for Uart, I would know that, and then I would protect them from the start. So: (I don't say it's the best way) If I have to move a whole buffer onto PortB, and protect two bits, then I would do it bitwise, ie. read bit in buffer, set/clear bit in PortB and ignore the bits I want to protect. Q.. -- 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

Note that : 1. The UART runs asyncronly in the "background" and may very well change the "value" of the rx/tx pins between your read-to-the-buffer and the write-back of the buffer. 2. The bcf/bsf always read/write 8 bits to/from the port, so what you are doing is actualy the same thing, only using more instructions. 3. The design of the B port protects the rx/tx pins when writing to the PORTB register anyway... Jan-Erik. Quentin wrote: {Quote hidden}> > > > > >Will i inject the wrong values into the uart by writing to the port or > >will the uart ignore my writes to the rx and tx bits (those bits will > >always be zero in the buffer )? > > > Normally, I won't be bothered to find out if it's going to be a problem > or not. If I am going to use two pins as TX/RX for Uart, I would know > that, and then I would protect them from the start. So: > (I don't say it's the best way) > If I have to move a whole buffer onto PortB, and protect two bits, then > I would do it bitwise, ie. read bit in buffer, set/clear bit in PortB > and ignore the bits I want to protect. > Q.. -- 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