nrf51822 fix UART error Rate / SPI?

[Daniel]

Hello,

i am new to nRF Bluetooth. My Setup ist:

One Atmel atmega640 and one nrf51822 communication via UART (at the moment).

I am sending data from atmega640 to the nrf and i am experiencing an error-rate about 10% in incoming Data in the nrf when using a UARt Datarate of 38400 baud, which seems to be normal without using Hardware FlowControl. (devzone.nordicsemi.com/.../)

My Problem is at the moment, that i need a communication with less Errors and higher DataRate, but there is already a Hardware, which i have to use with only two traces (RX/TX) between both chips. Additionally there is no HWFW available on Atmel's Atmega.

I am thinking about switching to SPI, where i can use the two existing UART traces (can i assign any pin for SPI on the nRF51822, too?) and manually solder two additional cables für SPI's "clk" and "ce". The nRF51822 would act as SPI Slave.

Is this a good idea? Will this work better or do i have to expect similar or other Problems when using Softdevice S110 with SPI? Which maximum datarates can i expect with SPI and ATMega640 (with 16MHz external Clock) as SPI-Master?

[Susheel Nuguru]

Hi Daniel,

you can use the UART pins to connect to the SPI, you then cannot use the the same pins with as UART. You also need to modify the SPI driver to use these pins instead of the default pin assignment.

Regarding the speed of SPI, If this is interrupt driven transfers then speeds over 1Mbps would overflow the buffers. There is a nice post by RK which will help you understand more about the SPI speed limitations. devzone.nordicsemi.com/.../