Datasheet

MSP430FR4133, MSP430FR4132, MSP430FR4131
www.ti.com SLAS865B –OCTOBER 2014–REVISED AUGUST 2015
Table 7-1. LCD_E Design Options
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
• 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
Internal Bias Generation
• 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 pins
• Higher current consumption than simply using V
CC
for the LCD driver
7.2.2.3 Detailed Design Procedure
A major component in designing the LCD solution is determining the exact connections between the
LCD_E peripheral module and the display itself. Two basic design processes can be employed for this
step, although often a balanced co-design approach is recommended:
• PCB layout-driven design
• Software-driven design
In the PCB layout-driven design process, LCD_E offers configurable segment Sx and common COMx
signals which are connected to the respective MSP430 device pins so that the routing of the PCB can be
optimized to minimize signal crossings and to keep signals on one side of the PCB only, typically the top
layer. For example, using a multiplexed LCD, it is possible to arbitrarily connect the Sx and COMx signals
between the LCD and the MSP430 device as long as segment lines are swapped with segment lines and
common lines are swapped with common lines. It is also possible to not contiguously connect all segment
lines but rather skip LCD_E module segment connections to optimize layout or to allow access to other
functions that may be multiplexed on a particular device port pin. Employing a purely layout-driven design
approach, however, can result in the LCD_E module control bits that are responsible for turning on and off
segments to appear scattered throughout the memory map of the LCD controller (LCDMx registers). This
approach potentially places a rather large burden on the software design that may also result in increased
energy consumption due to the computational overhead required to work with the LCD.
The other extreme is a purely software-driven approach that starts with the idea that control bits for LCD
segments that are frequently turned on and off together should be co-located in memory in the same
LCDMx register or in adjacent registers. For example, in case of a 4-mux display that contains several 7-
segment digits, from a software perspective it can be very desirable to control all 7 segments of each digit
though a single byte-wide access to an LCDMx register. And consecutive segments are mapped to
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