Software UART library

[nehallove]

Hi All,

We are trying to implement software Uart for our product because of some constraint. Does CCS has software library for software UART like MPLab that I can use?

Thank you.

Nehl
_________________
nehal

[temtronic]

Yes..it's in the manual...look under setup rs232(.....options....). Within design limits of the PIC you have, almost every I/O pin can be a UART.

hth
jay

[nehallove]

I am sharing I2C and software uart on the same pin. I am using
#use i2c(Master,Slow,sda=PIN_C4,scl=PIN_C3,force_hw,RESTART_WDT). How do I switch between UART and I2C at run time?

Thanks

nehl
_________________
nehal

[asmboy]

You need to tell which pic for instance to get a better sense of what to do
but trying to share with i2C is a tough place to be.

And showing a schematic of the circuit attached to you pic would not be a bad idea either.

[FvM]

Both software UART and I2C built-in functions are not prepared for dynamical pin sharing or e.g. re-initialization.

Basically, you would want to setup a software UART for the said pins, which are also hardware I2C pins according to your post. So hardware I2C functionalilty can be always achieved by accessing PIC special function registers, if the CCS I2C functions don't want to coexist with a software UART for the same pins, which I'm not sure about.

When switching from I2C to software UART, you'll need to re-initialize the port pins accordingly. So some low level action will be surely involved.

I wonder, how you want to use the pins as UART, if I2C peripherals are connected to it. They can easily block the pins, reacting on illegal I2C sequences.

[Ttelmah]

Realistically, the CCS software UART, has little needed in the way of 'setup'. For the output, the pin just needs to be set to drive high when not used, and for receive the pin just needs to be an input, and being pulled high by the external hardware before the receive functions are called.
Software I2C, as a master is similarly pretty friendly. The pins would need to be set to _float_ before I/O.
However mixing the two, will need a lot of care regarding the hardware I2C, is an 'open collector' bus, with the pins only ever driven low, and allowed to be pulled high with resistors. I can see problems mixing this onto either the receive line, or tx line for RS232, unless the hardware is physically disconnected when not in use.
Hardware I2C, will need you to set the TRIS to be set for both pins according to the data sheet for your particular chip, before use, and it would probably be best to turn off the peripheral before trying to use async serial on the pins. Unless the remote hardware is physically disconnected I can see problems occurring, if the serial is duplex, then the I2C condition that data on SDA must be stable when SCL is high, _will_ be breached, and I can quite easily see the lines generating an accidental 'start' condition, which could put the chips into an unknown state.
If this is 'simplex' serial, with just (say) the TX pin being used, then with care it could be made to work. Otherwise, it is an "accident waiting to happen".....
An alternative, would be to use a really simple PIC that has an I2C hardware peripheral as an I2C slave, and add it to the I2C bus, then have _it_ transmit/receive the serial needed under control of I2C.

Best Wishes

[nehallove]

Thank you very much for your reply guys. It was very informative and i have a clear idea it is illegal to share same bus for i2c and Uart devices without disconnecting devices. In my case that is not possible. As Ttelmah suggest I will look for i2c to uart converter/processor for UART I/O.

Thanks

nehl
_________________
nehal