SDI vs UART efficiency for wireless comms

[svjohngalt]

I am developing a wireless solution which will communicate at a lower data rate, 9600 or 19200. I see that Microchip has a nice module, MRF24J40MA with an SDI interface and STMicroelectronics has a module the SP1ML with a UART interface. I know they communicate in different frequency spectrum, but strictly from a programming and efficiency view point, which interface is better the SDI or UART?

I would like to know if anyone has used either of these devices and if so, how well did they work and what was the working range?

For my application, I need 40ft to 100ft and the use will be outside in barns which may have wifi. Yep, the horses get to browse the net instead of just standing there looking out at the greener pastors on the other side of the fence.

Thanks
George

[HenrikOlsson]

You mean SPI, not SDI right?
SDI is a serial interface generally used for video and runs in the hundreds of megbits per second range, I don't think a PIC will cope with that :-)

Technically, SPI being a sychronous protocol, is a bit more efficient since there's no need for start/stop bits so to transfer 8 bits you send 8 bits while with UART you have to actually send 10 bits to transfer 8 bits. This is ONLY for the interface between the uC and the module, it has NOTHING to do with how the module actually encodes and transfers the data over radio link.

SPI might also have an edge when it comes to variation in Clock frequency. If the respective oscillators for the uC and module drifts apart when using UART they might drift out of sync, that can't happen with SPI since it's synchronous.

With all this said and with the knowledge that PBP doesn't have any built in routines for "hardware SPI" like it has for hardware UART I'd say that USING a module with UART interface will be easier than one with a SPI interface.

The way that the module communicates with the uC has no bearing whatsoever on the range, speed or performance of the actual radio-link.

/Henrik.

[svjohngalt]

Sorry, yes SPI. I understand the uC interface has nothing to do with range but I am hoping someone out there has used one of these devices and may be familiar with them.

As it relates to efficiency, I am thinking mostly about the uC overhead for handline the SPI or UART in PBP. I like all the built in routines for UART but do they cause a lot of overhead or on a small application is the overhead so minimal as to not matter?


Thanks
George