MSP430FR6889 Datasheet, PDF (154/176 Pages) Texas Instruments – Mixed-Signal Microcontrollers

MSP430FR6889, MSP430FR68891, MSP430FR6888, MSP430FR6887
MSP430FR5889, MSP430FR58891, MSP430FR5888, MSP430FR5887
SLASE32A – AUGUST 2014 – REVISED MARCH 2015
www.ti.com
7.2.2 LCD_C Peripheral
7.2.2.1 Partial Schematic
Required LCD connections greatly vary by the type of display that is used (static or multiplexed), whether
external or internal biasing is used, and also whether the on-chip charge pump is employed. For any
display used, there is flexibility as to how the segment (Sx) and common (COMx) signals are connected to
the MCU which (assuming that the correct choices are made) can be advantageous for the PCB layout
and for the design of the application software.
Because LCD connections are application specific, it is difficult to provide a single one-fits-all schematic.
However, for an example of connecting a 4-mux LCD with 40 segment lines that has a total of
4 × 40 = 160 individually addressable LCD segments to an MSP430FR6989, see the Gas or Water Meter
with 2 LC Sensors Reference Design (TIDM-LC-WATERMTR).
7.2.2.2 Design Requirements
Due to the flexibility of the LCD_C peripheral module to accommodate various segment-based LCDs,
selecting the right display for the application in combination with determining specific design requirements
is often an iterative process. There can be well-defined requirements in terms of how many individually
addressable LCD segments need to be controlled, what the requirements for LCD contrast are, which
device pins are available for LCD use and which are required by other application functions, and what the
power budget is, to name just a few. TI strongly recommends reviewing the LCD_C peripheral module
chapter in the MSP430FR58xx, MSP430FR59xx, MSP430FR68xx, and MSP430FR69xx Family User's
Guide (SLAU367) during the initial design requirements and decision process. The following table
provides a brief overview over different choices that can be made and their impact.
OPTION OR FEATURE
IMPACT OR USE CASE
Multiplexed LCD
• Enable displays with more segments
• Use fewer device pins
• LCD contrast decreases as mux level increases
• Power consumption increases with mux level
• Requires multiple intermediate bias voltages
Static LCD
Internal Bias Generation
• Limited number of segments that can be addressed
• Use a relatively large number of device pins
• Use the least amount of power
• Use only V_CC and GND to drive LCD signals
• Simpler solution – no external circuitry
• Independent of V_LCD source
• Somewhat higher power consumption
External Bias Generation
• Requires external resistor ladder divider
• Resistor size depends on display
• Ability to adjust drive strength to optimize tradeoff between power consumption and good drive of large
segments (high capacitive load)
• External resistor ladder divider can be stabilized through capacitors to reduce ripple
Internal Charge Pump
• Helps ensure a constant level of contrast despite decaying supply voltage conditions (battery-powered
applications)
• Programmable voltage levels allow software-driven contrast control
• Requires an external capacitor on the LCDCAP pin
• Higher current consumption than simply using V_CC for the LCD driver
154 Applications, Implementation, and Layout
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