SPI and USART conflict question

garryp4 · Post by **garryp4** » Tue Jul 17, 2007 10:19 pm

The 18F4550 RC7 is both the USART TX and the SPI SDO. Can I 'include' both these with out any conflict? How much of a speed penalty does the software SPI cause? I am in the process of laying out a circuit so need to know before shipping off the gerber files. Any help is greatly appreciated.

Thanks.

TimB · Post by **TimB** » Tue Jul 17, 2007 10:41 pm

In software its simply a mater of checking a flag to tell the source of the interrupt, however you will confuse the poor pic with the use of both a Usart and a SPI on the same pin.

garryp4 · Post by **garryp4** » Wed Jul 18, 2007 4:07 am

I will use the software SPI for the memory.

Thanks.

TimB · Post by **TimB** » Wed Jul 18, 2007 7:08 am

Are you not going to confuse the device on the other end of the USART?

David Barker · Post by **David Barker** » Wed Jul 18, 2007 7:30 am

You really don't want to mix the two functions on the same pin. Look at using a different pin with software SPI connected to your external memory device. Writing to these devices usually takes a few ms, so I wouldn't worry too much about software SPI speed (although it is pretty good as it doesn't use indirect addressing)

Look at '24LC640.bas', located in the samples folder for pointers...