Part Number: MSP430F5132
Hi Experts!
How can I use the resistor ladder to set my desired comparator reference voltage? I can't find in datasheet.
In section 32.2.6 of MSP430x5xx and MSP430x6xx Family User's Guide, there is a diagram of the Comparator_B resistor ladder controlled by CBREF1 and CBREF0:
How can I use CBREF1 and CBREF0 to achieve my desired comparator Vref?
I'm hoping for an equation like Vref0 = [CBREF0] * Vin and Vref1 = [CBREF1] * Vin or something.
The example code found below is the only example using the R-ladder (line 38). Unfortunately, this doesn't help me understand how to achieve a Vref0 or Vref1. Hoping for any clarification!
// MSP430F51x2 Demo - COMPB Toggle from LPM4; CompB in ultra low power mode
// Vcompare is compared against the Vcc*1/2
//
// Description: Use CompB and shared reference to determine if input 'Vcompare'
// is high/low. When Vcompare exceeds 0.5*Vcc CBOUT goes high and when
// Vcompare is less than 0.5*Vcc then CBOUT goes low.
// Connect P3.3/CBOUT to P1.0 externally to see the LED toggle accordingly.
//
// MSP430F51x2
// ------------------
// /|\| |
// | | |
// --|RST P1.1/CB1 |<--Vcompare
// | |
// | P3.3/CBOUT|----> 'high'(Vcompare>Vcc*0.5); 'low'(Vcompare<Vcc*0.5)
// | | |
// | P1.0 |__| LED 'ON'(Vcompare>Vcc*0.5); 'OFF'(Vcompare<Vcc*0.5)
// | |
//
// C.Sterzik/B.Nisarga
// Texas Instruments Inc.
// Dec 2009
// Built with CCS v4 and IAR Embedded Workbench Version: 4.21
//******************************************************************************
#include <msp430.h>
int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
P3DIR |= BIT3; // P3.3 output direction
P3SEL |= BIT3; // Select CBOUT function on P3.3/CBOUT
// Setup ComparatorB
CBCTL0 |= CBIPEN+CBIPSEL_1; // Enable V+, input channel CB1
CBCTL1 |= CBMRVS; // CMRVL selects the refV - VREF0
CBCTL1 |= CBPWRMD_2; // Ultra-Low Power mode
CBCTL2 |= CBRSEL; // VREF is applied to -terminal
CBCTL2 |= CBRS_1+CBREF04; // VCC applied to R-ladder; VREF0 is Vcc*1/2
CBCTL3 |= BIT1; // Input Buffer Disable @P1.1/CB1
CBCTL1 |= CBON; // Turn On ComparatorB
__delay_cycles(75); // delay for the reference to settle
__bis_SR_register(LPM4_bits); // Enter LPM4
__no_operation(); // For debug
}Thank you!
