I’ve taken this from the design recommendations for custom expansion boards on the Gumstix site:
“4. Noise on the UART_RX3 line during boot can interrupt the normal booting sequence. Consider adding a pull-up resistor to a SYSEN-gated 1.8V supply on this line.”
Can anyone tell me what this means?
This isn’t implemented on the Tobi board, there are no pull-ups. The Tobi board leaves the UART_RX3 line floating until its gate is enabled by SYSEN. Is this what’s recommended? Or do you enable the 1.8 volt supply straight away (and thus the gate) and pull up UART_RX3 to 1.8 volts? Which would tend to contradict:
“1. Use the SYSEN line to protect any IO pins to the OMAP CPU. SYSEN is brought high when the Overo is ready to communicate; driving GPIOs before this point can damage the processor.”