S32K116 UART Communication protocol emulation over FLEXIO

[jayashreepasane]

I'm trying to emulate UART over flexi on the S32116EVB developer kit. I want to keep the TX of UART by default high (open drain) and then start putting data on tx line. As explained in the reference manual I have the following bits in the register to make it supprort opendrain. 

FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINCFG (0x01);
FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINPOL (0x01);

When I do the setting as mentioned above in the register , TX line remains at low state and no communication happens (failed to transmit) 

I want to set the state of the pin to default high. and start transmission over tx line, Currently this is not possible without external pull up resistor. 

So can anyone tell me, if it is true that I always need an external pullup register to achieve communication as given in the above picture?

I am attaching my sample setting too for tx line

clock enable

PCC-> PCCn [PCC_PORTA_INDEX] | = 1 << PCC_PCCn_CGC_SHIFT;
// PORTD_0 set as FLEXIO
PORTD-> PCR [2] | = 0x00000400; / * Port D2: MUX = FLEXIO * / 

// Enable clock to the FXIO
(PCC-> PCCn [PCC_FlexIO_INDEX]) | = 0x41000000;

FLEXIO-> CTRL | = FLEXIO_CTRL_DBGE (1);
FLEXIO-> SHIFTSTAT = 0x0F;

// TRANSMITTER
// shifter configuration
FLEXIO-> SHIFTCTL [0] | = (FLEXIO_SHIFTCTL_TIMSEL (0) | FLEXIO_SHIFTCTL_TIMPOL (0) | FLEXIO_SHIFTCTL_PINSEL (0x03) | FLEXIO_SHIFTCTL_SMOD (0x02));
FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINCFG (0x01);
FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINPOL (0x01);
FLEXIO-> SHIFTCFG [0] | = (FLEXIO_SHIFTCFG_INSRC (0) | FLEXIO_SHIFTCFG_SSTOP (0x03) | FLEXIO_SHIFTCFG_SSTART (0x02));
// set baud rate
// FLEXIO-> TIMCMP [0] = 0x00000F04;
// timer configuration
FLEXIO-> TIMCFG [0] | = (FLEXIO_TIMCFG_TIMOUT (0) | FLEXIO_TIMCFG_TIMDEC (0) | FLEXIO_TIMCFG_TIMDIS (0x02) | FLEXIO_TIMCFG_TIMENA (0x02) | FLEXIO_TIMCFG_TSTOP (0x02) | FLEXIO_TIMCFG_TSTART (0x01));

[jorge_a_vazquez]

Hi Jayashree pasane

PINCFG and PINPOL are for the logical behaves of the pin, but as long as you are using this pin as open drain, it will need a pull up to work. You can use the internall pullup of the MCU, it is enabled with the PE and PS of the PORT_PCRn field.

Hope this helps

Best regards
TIC

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[jayashreepasane]

Hello Jorge,

Thank you again for the response.

I tried to enable the internal pull up, but still I face the same issue. I am trying to use Evaluation board S32K116EVB. 

Regards,

Jayashree P

[jorge_a_vazquez]

Hi jayashree pasane

In order to have the flexIO TX of UART by default high you need to set:

FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINCFG (0x00);
FLEXIO-> SHIFTCTL [0] | = FLEXIO_SHIFTCTL_PINPOL (0x03);

With this config, you will have TX high by default and when transmission happens, it will act as your second scope.

Regards

Jorge Alcala