nRF51822 doesn't start if UART RX pin is connected

[sunil kumar]

Iam using softdivice 110 and sdk 10.0.0, when i connect UART RX pin to TX of STN1110 the processor doesn't start until I remove connection between RX of nRF51822 and TX of STN1110(TX of nRF51822 and RX of STN1110 are connected), once i remove the connection(RX of nRF51822 and TX of STN1110) the nRF51822 starts and it is not effected if i later connect them, I tried pin p0.0 and p0.8(as RX pins) same result in both case, and i cannot configure STN1110, kindly help me. It is getting stuck in SOFTDEVICE_HANDLER_INIT in ble_stack_init().

[Alex]

When disconnected, what is the voltage on Tx of STN1110 and what is voltage of PSU for nRF?

[sunil kumar]

I correct myself, the processor starts but it restarts while initializing softdevice, in softdevice_handler_init() function the breakpoint at function sd_softdevice_enable() will hit, after this function the processor will restart. The voltage at Tx of STN1110 is 0.7V and at PSU for nRF is 3.3V.

[sunil kumar]

for calling SOFTDEVICE_HANDLER_INIT iam using "NRF_CLOCK_LFCLKSRC_XTAL_20_PPM" as clock source.

[Ole Bauck]

The default configuration for the SDK examples is that they will reset when the code meets an error condition, see here. So probably the sd_softdevice_enable function returns an error. Check if this is the case and what the error code is.

Are you using the uart driver from the SDK (app_uart_fifo)?

[sunil kumar]

Yes iam using uart driver from SDK, uart code is same has that of ble_app_uart example code. What causes that error. how should i overcome it.