Send UART break

RE: Send UART break

ScruffR — Mon, 11 Nov 2019 17:06:56 GMT

Thanks for the reply!

The 100µs + 12µs were meant to reflect the minimum lengths (plus some extra) and a "normal" reconfiguration did cause some unexpected noise on the lines, but since asking this question I've done some more digging and came up with an alternative "workaround" shown in my other question about 2 stop bit configuration here

https://devzone.nordicsemi.com/f/nordic-q-a/54215/howto-use-uarte-250000-8n2-plus-txbreak-for-dmx512-protocol

In a nutshell I just disable the interface via `NRF_UARTE0->ENABLE = 0`, set the TX pin LOW, wait for a variable time and then reenable via `NRF_UARTE0->ENABLE = 8`. The reenabling takes about 14µs which works well with the min. 12µs MAB.

RE: Send UART break

Turbo J — Mon, 11 Nov 2019 14:23:07 GMT

The MAB (Mark-after-break) is usually specified variable length (with a minimum) for DMX512.The devices on the bus simply wait for the next start bit.

If you really needed that tight timing consider using the PWM peripherial in order to create the waveform.

RE: Send UART break

ScruffR — Sun, 10 Nov 2019 15:22:26 GMT

Sorry for resurrecting this thread.

I have a similar problem but the proposed solution won't work with that as it would break the timing requirements.

In order to facilitate UARTE0 (at 250000 baud with 8bit no parity 2 stop bits) as a DMX512 controller I'd need a 100µs LOW 12µs HIGH level on the TX pin immediately followed by an up to 513 byte data train.

So reconfiguring the interface won't be an option.

Are there any alternative solutions?

BTW, I'm also faced with the problem that `nrf_uarte_configure()` doesn't seem to provide an option for setting 2 stop bits.

RE: Send UART break

awneil — Fri, 30 Aug 2019 16:44:57 GMT

Sending 0x00 at the correct baud rate should not be interpreted as a Break - because of the Start & Stop bits.

But Turbo J's suggestion to use a way-too-low baud rate is a good one - unless this mystery "modem" is already running at a very slow speed ...

RE: Send UART break

Turbo J — Fri, 30 Aug 2019 14:41:57 GMT

Dead simple: Program the lowest baud rate that the UART(E) peripherial supports, and then send a 0x00 byte.

If you cannot go low enough, re-program the IO pin to be normal GPIO output and pull it down manually - you will need a way to keep track of time, too.

RE: Send UART break

endian-benjamin — Fri, 30 Aug 2019 13:16:22 GMT

So it's not the case that a break is sent if you for example suspend the UART and then resume it?f

RE: Send UART break

Edvin — Fri, 30 Aug 2019 12:48:28 GMT

I don't know how your device interprets it, but according to the page that I linked, it may be sufficient to just send a 0x00. If not you have to do something else. It may be just as easy to disable the UART, set it to low, wait for a while (a bit more than one byte with the baudrate that you use, and turn the UART back on. I don't have the modem that you speak of, so I can't test it, but you can try to analyze the GPIO with a logic analyzer to see that it behaves like you want to.

RE: Send UART break

endian-benjamin — Fri, 30 Aug 2019 12:05:11 GMT

Yeah the plan B is to reconfigure the baudrate to something very low and send 0x00. It feels pretty hacky tho :P

RE: Send UART break

Edvin — Fri, 30 Aug 2019 12:00:07 GMT

Hello,

I am not sure exactly what sort of device that is, but it looks like from here, that a break is the line being held low.

You can try to send a UART string containing 0x00's, and see if that triggers the modem to wake up.

If not, a UART break condition is just the line held low, so you can try to disable the UART, set the pin as an output, put it in logic low (set it to 0. You can use nrf_gpio_pin_clear(pin_number)).

But first, try to send a string containing some 0x00's.

Best regards,

Edvin

Best regards,

Edvin