SLAU367P October 2012 – April 2020 MSP430FR5041 , MSP430FR5043 , MSP430FR50431 , MSP430FR5847 , MSP430FR58471 , MSP430FR5848 , MSP430FR5849 , MSP430FR5857 , MSP430FR5858 , MSP430FR5859 , MSP430FR5867 , MSP430FR58671 , MSP430FR5868 , MSP430FR5869 , MSP430FR5870 , MSP430FR5872 , MSP430FR58721 , MSP430FR5887 , MSP430FR5888 , MSP430FR5889 , MSP430FR58891 , MSP430FR5922 , MSP430FR59221 , MSP430FR5947 , MSP430FR59471 , MSP430FR5948 , MSP430FR5949 , MSP430FR5957 , MSP430FR5958 , MSP430FR5959 , MSP430FR5962 , MSP430FR5964 , MSP430FR5967 , MSP430FR5968 , MSP430FR5969 , MSP430FR5969-SP , MSP430FR59691 , MSP430FR5970 , MSP430FR5972 , MSP430FR59721 , MSP430FR5986 , MSP430FR5987 , MSP430FR5988 , MSP430FR5989 , MSP430FR5989-EP , MSP430FR59891 , MSP430FR5992 , MSP430FR5994 , MSP430FR59941 , MSP430FR6005 , MSP430FR6007 , MSP430FR6035 , MSP430FR6037 , MSP430FR60371 , MSP430FR6041 , MSP430FR6043 , MSP430FR60431 , MSP430FR6045 , MSP430FR6047 , MSP430FR60471 , MSP430FR6820 , MSP430FR6822 , MSP430FR68221 , MSP430FR6870 , MSP430FR6872 , MSP430FR68721 , MSP430FR6877 , MSP430FR6879 , MSP430FR68791 , MSP430FR6887 , MSP430FR6888 , MSP430FR6889 , MSP430FR68891 , MSP430FR6920 , MSP430FR6922 , MSP430FR69221 , MSP430FR6927 , MSP430FR69271 , MSP430FR6928 , MSP430FR6970 , MSP430FR6972 , MSP430FR69721 , MSP430FR6977 , MSP430FR6979 , MSP430FR69791 , MSP430FR6987 , MSP430FR6988 , MSP430FR6989 , MSP430FR69891
The peak voltage of the output waveforms together with the selected mode and biasing determine the contrast and the contrast ratio of the LCD. The LCD contrast can be controlled in software by adjusting the LCD voltage generated by the integrated charge pump using the VLCDx settings.
The contrast ratio depends on the used LCD display and the selected biasing scheme. Table 36-3 shows the biasing configurations that apply to the different modes together with the RMS voltages for the segments turned on (VRMS,ON) and turned off (VRMS,OFF) as functions of VLCD. It also shows the resulting contrast ratios between the on and off states.
| Mode | Bias Config | LCDMx | LCD2B | COM Lines | Voltage Levels | VRMS,OFF/ VLCD | VRMS,ON/ VLCD | Contrast Ratio VRMS,ON/ VRMS,OFF |
|---|---|---|---|---|---|---|---|---|
| Static | Static | 0000 | X | 1 | V1, V5 | 0 | 1 | 1/0 |
| 2-mux | 1/2 (1) | 0001 | 1 | 2 | V1, V3, V5 | 0.354 | 0.791 | 2.236 |
| 1/3 | 0001 | 0 | 2 | V1, V2, V4, V5 | 0.333 | 0.745 | 2.236 | |
| 3-mux | 1/2 | 0010 | 1 | 3 | V1, V3, V5 | 0.408 | 0.707 | 1.732 |
| 1/3 (1) | 0010 | 0 | 3 | V1, V2, V4, V5 | 0.333 | 0.638 | 1.915 | |
| 4-mux | 1/2 | 0011 | 1 | 4 | V1, V3, V5 | 0.433 | 0.661 | 1.528 |
| 1/3 (1) | 0011 | 0 | 4 | V1, V2, V4, V5 | 0.333 | 0.577 | 1.732 | |
| 5-mux | 1/3 (1) | 0100 | 0 | 5 | V1, V2, V4, V5 | 0.333 | 0.537 | 1.612 |
| 6-mux | 1/3 (1) | 0101 | 0 | 6 | V1, V2, V4, V5 | 0.333 | 0.509 | 1.528 |
| 7-mux | 1/3(1) | 0110 | 0 | 7 | V1, V2, V4, V5 | 0.333 | 0.488 | 1.464 |
| 8-mux | 1/3(1) | 0111 | 0 | 8 | V1, V2, V4, V5 | 0.333 | 0.471 | 1.414 |
A typical approach to determine the required VLCD is by equating VRMS,OFF with a LCD threshold voltage provided by the LCD manufacturer, for example when the LCD exhibits approximately 10% contrast (Vth,10%): VRMS,OFF = Vth,10%. Using the values for VRMS,OFF/VLCD provided in the table results in VLCD = Vth,10%/(VRMS,OFF/VLCD). In the static mode, a suitable choice is VLCD greater than or equal to three times Vth,10%.
In 3-mux and 4-mux mode, a 1/3 biasing is typically used, but a 1/2 biasing scheme is also possible. The 1/2 bias reduces the contrast ratio, but the advantage is a reduction of the required full-scale LCD voltage VLCD.