Serial com with internal oscillator

[mikendee]

Hi Mister-e
Thanks for the reply.

My question with the AUSART is. I have to us SHIFTIN and SHIFTOUT to talk to the AD7730 and Serout2 to send the result to another Pic.

Can I use Shiftout with RB1/SDO, RB2/SDI and RB4/SCK and SEROUT or HSEROUT with RB5/TX?

If I did this would the TXSTA register have to be changed between transmissions or would it be better to use another pin?

[Ron Marcus]

I have spent days collectively trying to work with async comms and no xtal. I can get lucky, but for a customer app. I would always revert to a crystal Why not use SPI for both. Use one pin to select your other PIC, and one to select your peripheral.Or, if the peripheral is looking for a low to select, set your outlying PIC as an enable high, and use the same pin. Just make sure both external units go into high impedance when deselected. I did this with a video on screen display. The PIC generating the overlay could only grab a little info between frames. I used shiftin and shiftout with very reliable results. Async can be unreliable even with a crystal in noisy environs, but makes it easy to hook up to a PC or GPS engine, etc...

Ron

[mikendee]

Hi Ron,

I think this will be the solution for me. I will have to use an extra pin to select the AD7730 but then I have 2 extras from not using an xtal. I can't see whether it is high impedance when not selected from the Datasheet but will check in a breadboard to see. I'll have to learn to use a pic as a slave in SPI but hopefully that won't be too tricky.

Thankyou both for your help. I'd be stumbling around in the dark without it.

Thanks,

Mike

[mister_e]

SPI or I2C, synchronous serial communication is really the way to go with an internal oscillator. If you're using SPI/I2C device, no harm to use the internal oscillator as it's a synchronous communication, but for RS232 asynch... this will cause you problem one day or another... unless you're really lucky!