Serial.end()?

Forum 2005-2010 (read only) Software Development
1

Hi All,

I need to use digital pins 0 and 1 for BOTH serial communication and digital i/o.. I will need to toggle between these two uses programmatically..

I noticed in the reference that once I call Serial.begin, I am told not to use these pins for digital i/o.. This is obviously not a limitation of the Atmega.. So, since there is Serial.begin, is there effectively a Serial.end? Can I just call pinMode(0,INPUT) and pinMode(1,INPUT) after I'm done using these pins for serial comm? I poked around in the source a bit but beginSerial() in wiring_serial.c is using assembly macros and pinMode isn't.. It's not exactly clean enough for me to be sure what's happening, so I thought I'd ask..

Thanks,
ed

2

On the 168, there is an interrupt enabled when you include serial:
sbi(UCSR0B, RXCIE0);

so, if it is possible to do what you want, you should CLI that interrupt flag when you are not in serial mode

caveats:

  1. you might have some cleanup/flushing to do when switching between serial and pin

  2. any external devices connected to serial are likely to get confused.

  3. this is implementation dependent, expect it to break with the next arduino release.

3

...expect it to break with the next arduino release.

Unless ofcourse, it is part of the core to implement such a thing as end();

I think it sounds like a good idea.

4

Thanks AlphaBeta and dcb..

Well my thought is that unless there is some implicit Serial.end() (like simply calling pinMode does the same thing) then we should have a Serial.end().. But even if I code it, we would need good reasons for it to be in the core..

I have a special case where I'm using the UART to implement a custom 1 wire bus and I need to use the digital input to sense if another node is communicating on the bus.. But what about other more "typical" cases?

I'll start the list..

  1. A datalogger that can automatically switch between datalogger and datadump modes.. It would call Serial.begin() and send some byte(s) at restart and then wait for a specific response.. If the correct response is not received from the datadump PC application the device goes into datalogging mode by calling Serial.end() and pins 0 and 1 are used as input.. Otherwise pins 0 and 1 are used for Serial comm..

  2. ?

  3. ?

Any more ideas that would support including a Serial.end()?

Thanks,
ed

5

Good luck :slight_smile:

6

It can be very handy to have a software interrupt that triggers when a specific byte has been received. For example, a carriage return character (13). This lets you process a receive buffer only after a full line has been received, instead of having to watch and process every received byte in realtime. Even better, watching for several characters, or a specific pause in transmission (handy for MODBUS RTU).