LPC824 - RTS/OEPOL problem related to Errata sheet?

[lpcware]

Content originally posted in LPCWare by Wojtkingson on Thu Jul 02 08:58:01 MST 2015
Hi!

I have little problem with driving my RS485 transceiver via RTS signal.

RTS signal - PIO0_8
1) fixed functions ACMP_I2, CLKIN are disabled via SWM

2) RTS function assigned to pin

Chip_SWM_MovablePinAssign(usart->swmRTS, usart->rtsPin);

3) OESEL bit set - for RTS as RS485 tx enable signal

Chip_UART_ConfigData(usart->lpcUsartNumber, (UART_CFG_DATALEN_8 | UART_CFG_PARITY_NONE | UART_CFG_STOPLEN_1 | UART_CFG_OESEL | UART_CFG_OEPOL));

RTS signal is measured directly on MCU pin without RS485 transceiver

With OEPOL = 1 and defacto same with OEPOL = 0, RTS signal is blue
[img=1600x898]http://tinypic.com/r/2z5t0l4/8[/img]



Problem:
1) Voltage level on RTS
2) Generally strange shape of RTS signal - maybe problem which is related to ERRATAsheet with TXIDLE
3) When i change setting of OEPOL, polarity didnt change

[lpcware]

Content originally posted in LPCWare by starblue on Thu Jul 02 11:34:21 MST 2015

---

Quote: Wojtkingson
1) Voltage level on RTS
2) Generally strange shape of RTS signal

---

Such a slowly moving signal usually indicates High-Z state (confused me as well when I saw it for the first time), so you may need to add a pull-up. Maybe that also corrects the voltage.