The LCD of my MSP430 development board doesn't work when voltage biases are generated externally

Question

I am programming the LCD of my MSP430FR6989 development board (MSP-EXP430FR6989), and I have a question regarding generating VLCD (V1) and LCD biasing.

The development board got a 14-segment, 6 digit LCD connected to the MSP430 (MSP-EXP40FR6989 User Guide pg 11/41), and the MSP430 got an LCD module (LCD_B and LCD_C module).

In order to turn on a segment, we set the relevant segment line (Sx) and the COM line (COMx), by writing a certain word to the LCDCMEMx registers.

These are the things we need to configure before writing values into the LCDCMEMx registers:

• Set th Vlcd (V1) to be sourced from internally from the charge pump or externally.
• set the value of Vlcd (V1)
• set the bias, 1/2 bias or 1/3 bias.
• configure the source of V2 - V4, internally or externally (R23 pin, R13/LCDREF pin, R03 pin)
• Source V5 from Vss or from external R03 pin
• set the LCD's frequency (flcd)
• Add a capacitor to the LCDCAP/R33 pin.
• set the correct segments and COMs using the LCDCMEMx registers
• Turn on the LCD

I would like to have V1 sourced internally, 1/3 bias, V2 - V4 sourced externally from R23 and R13/LCDREF pins, V5 sourced from R03 pin, flcd = 512Hz, Vlcd (V1) = 3.44V, the MSP-EXP430FR6989 has a capacitor and resistor network attached to it (MSP-EXP430FR6989 User Guide pg 29/41).

As you can see in the code below this is the value written to LCDCVCTL (SFR responsible for the LCD_C module's voltage) LCDCVCTL = 0x1E68 which is 0001 1110 0110 1000

That is the code relevant to the LCD Voltage and bias generation FYI

#include <msp430.h> 

//code

#define ENABLE_PINS 0xFFFE

#define TURN_ON_LCD     (LCDCCTL0 |= LCDON)
#define TURN_OFF_LCD    (LCDCCTL0 &= (~LCDON))
#define CLEAR_LCD_MEM   (LCDCMEMCTL |= LCDCLRM)

//code

void init_LCD (void);
void show_Char (unsigned char ch, unsigned int pos);

inside main () function

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;   // stop watchdog timer
    PM5CTL0 = ENABLE_PINS;

    //code
    init_LCD ();

    show_Char('F',1);
    show_Char('O',2);
    show_Char('R',3);
    show_Char('A',4);
    show_Char('T',5);

    TURN_ON_LCD;

    while(1);

    return 0;
}

Inside the init_LCD ()

void init_LCD (void)
{
     //code

    //configuring: COM0 COM1 COM2 COM3
    //R23 R13/LCDREF R03
    P6SEL1 |= (BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6);
    P6SEL0 |= (BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6);

    LCDCCTL0 = (LCDPRE__16 | LCDDIV_3 | LCD4MUX | LCDLP);

    LCDCVCTL = 0x1E68;//external biasing
    //VLCD = 1111, LCDCPEN = 1, VLCDREF = 00, VLCD = 3.44V
    //R03EXT = 1, V5 sourced from R03 pin
    //LCDEXTBIAS = 1, V2 - V4 sourced externally, and internal bias generator is switched off
    //VLCDEXT = 0, VLCD (V1) is sourced internally from the Charge Pump
    //LCDPEN = 1, Charge Pump is enabled
    //LCD2B = 0, 1/3 Bias



    //LCDCVCTL = 0x1E08; //V2 - V4 generated internally

    LCDCCPCTL = LCDCPCLKSYNC;//TI

    CLEAR_LCD_MEM;

}

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However, when I build and download the code into the development board, I don't see any segments being turned ON.

I changed the code to configure the LCD's bias to be sourced internally LCDCVCTL = 0x1E08 which is 0001 1110 0000 1000, and the LCD segments got turned ON.

LCDCVCTL = 0x1E08;
//VLCD = 3.44V
//Charge Pump enabled
//V1 generated internally
//V2 - V4

---

Kindly help me with this issue

Documents I used for reference:

• Designing with MSP430 MCUs and Segment LCD Application Note
• MSP-EXP430FR6989 User Guide
• MSP430FR6989 User Guide
• MSP430FR6989 Datasheet