Part Number: MSP432P401R
Hello!
I am having a bit of a problem setting up an SPI transmission with an MSP432 microcontroller.
I am quite new to this controller, so maybe this question is obvious.
Basically I am trying to drive an EA DOGL-128 graphical LCD display with SPI interface.
This is how the spi interface is initialised:
#include <driverlib.h>
#include <spi_drv.h>
/* SPI Master Configuration Parameter */
const eUSCI_SPI_MasterConfig spiMasterConfig =
{
EUSCI_B_SPI_CLOCKSOURCE_SMCLK, // SMCLK Clock Source
12000000, // SMCLK = DCO = 12MHZ
10000, // SPICLK = 10khz
EUSCI_B_SPI_MSB_FIRST, // MSB First
EUSCI_B_SPI_PHASE_DATA_CHANGED_ONFIRST_CAPTURED_ON_NEXT, // Phase
EUSCI_B_SPI_CLOCKPOLARITY_INACTIVITY_HIGH, // High polarity
EUSCI_B_SPI_3PIN // 3Wire SPI Mode
};
Public void spi_init(void)
{
/* Selecting P1.5 and P1.6 in SPI mode */
GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P1,
GPIO_PIN5 | GPIO_PIN6 , GPIO_PRIMARY_MODULE_FUNCTION);
// Set pin 4.3 as CS pin.
GPIO_setAsOutputPin(GPIO_PORT_P4, GPIO_PIN3);
/* We should give a falling edge to CS pin, not entirely sure if this is necessary. */
/* Possibly we might have to catch the transmit interrupt and then control CS??? Not yet sure how this works. */
GPIO_setOutputHighOnPin(GPIO_PORT_P4, GPIO_PIN3);
/* Configuring SPI in 3wire master mode */
SPI_initMaster(EUSCI_B0_BASE, &spiMasterConfig);
/* Enable SPI module */
SPI_enableModule(EUSCI_B0_BASE);
}
And this is what the transmit function looks like:
Public void spi_transmit_byte(U8 byte)
{
/* Polling to see if the TX buffer is ready */
while (!(SPI_getInterruptStatus(EUSCI_B0_BASE,EUSCI_B_SPI_TRANSMIT_INTERRUPT)));
/* Transmitting data to slave */
SPI_transmitData(EUSCI_B0_BASE, byte);
}
Now the SPI transmission itself works OK, checked with a logic analyser and it seems there is no problem with it.
The problem is that the LCD has an A0 pin that basically determines if the command I am sending should be interpreted
as writing data or as a command. The A0 pin needs to be set low/high at the end of the SPI byte transmission.
I tried controlling it like this at first:
Private void disp_command(U8 cmd, Boolean reg_select)
{
if (reg_select)
{
GPIO_setOutputHighOnPin(GPIO_PORT_P1, GPIO_PIN7);
}
else
{
GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN7);
}
spi_transmit_byte(cmd);
}
But this did not work, because the A0 pin got set before the previous byte was finished sending.
So I tried to set A0 in the spi_transmit_byte function.
Public void spi_transmit_byte(U8 byte, Boolean reg_select)
{
/* Polling to see if the TX buffer is ready */
while (!(SPI_getInterruptStatus(EUSCI_B0_BASE,EUSCI_B_SPI_TRANSMIT_INTERRUPT)));
/* Transmitting data to slave */
if (reg_select)
{
GPIO_setOutputHighOnPin(GPIO_PORT_P1, GPIO_PIN7);
}
else
{
GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN7);
}
SPI_transmitData(EUSCI_B0_BASE, byte);
}
However in this case A0 is also set at the wrong time. More exactly it is set during the PREVIOUS
byte, so the transmission isn't correct. Basically the way I understand it, is that the EUSCI_B_SPI_TRANSMIT_INTERRUPT is raised
when the SPI interface is ready for a new byte, but the old one hasn't finished sending yet. What I need to do is somehow catch the moment
when the MCU starts to actually send a byte and then control the A0 pin. Right now I don't see a good way of doing this. maybe somebody has experience with a similar problem.
PS! In the code there are the following defines:
#define Public
#define Private static
