SLAA654A November   2014  – July 2015 CC430F6147 , MSP430F412 , MSP430F413 , MSP430F4132 , MSP430F415 , MSP430F4152 , MSP430F417 , MSP430F423A , MSP430F4250 , MSP430F425A , MSP430F4260 , MSP430F4270 , MSP430F427A , MSP430F435 , MSP430F4351 , MSP430F436 , MSP430F4361 , MSP430F437 , MSP430F4371 , MSP430F438 , MSP430F439 , MSP430F447 , MSP430F448 , MSP430F4481 , MSP430F449 , MSP430F4491 , MSP430F4616 , MSP430F46161 , MSP430F4617 , MSP430F46171 , MSP430F4618 , MSP430F46181 , MSP430F4619 , MSP430F46191 , MSP430F47126 , MSP430F47127 , MSP430F47163 , MSP430F47166 , MSP430F47167 , MSP430F47173 , MSP430F47176 , MSP430F47177 , MSP430F47183 , MSP430F47186 , MSP430F47187 , MSP430F47193 , MSP430F47196 , MSP430F47197 , MSP430F477 , MSP430F478 , MSP430F4783 , MSP430F4784 , MSP430F479 , MSP430F4793 , MSP430F4794 , MSP430F6433 , MSP430F6435 , MSP430F6436 , MSP430F6438 , MSP430F6458 , MSP430F6459 , MSP430F6630 , MSP430F6631 , MSP430F6632 , MSP430F6633 , MSP430F6634 , MSP430F6635 , MSP430F6636 , MSP430F6637 , MSP430F6638 , MSP430F6658 , MSP430F6659 , MSP430F6720 , MSP430F6720A , MSP430F6721 , MSP430F6721A , MSP430F6723 , MSP430F6723A , MSP430F6724 , MSP430F6724A , MSP430F6725 , MSP430F6725A , MSP430F6726 , MSP430F6726A , MSP430F6730 , MSP430F6730A , MSP430F6731 , MSP430F6731A , MSP430F6733 , MSP430F6733A , MSP430F6734 , MSP430F6734A , MSP430F6735 , MSP430F6735A , MSP430F6736 , MSP430F6736A , MSP430F6745 , MSP430F67451 , MSP430F67451A , MSP430F6745A , MSP430F6746 , MSP430F67461 , MSP430F67461A , MSP430F6746A , MSP430F6747 , MSP430F67471 , MSP430F67471A , MSP430F6747A , MSP430F6748 , MSP430F67481 , MSP430F67481A , MSP430F6748A , MSP430F6749 , MSP430F67491 , MSP430F67491A , MSP430F6749A , MSP430F67621 , MSP430F67621A , MSP430F67641 , MSP430F67641A , MSP430F6765 , MSP430F67651 , MSP430F67651A , MSP430F6765A , MSP430F6766 , MSP430F67661 , MSP430F67661A , MSP430F6766A , MSP430F6767 , MSP430F67671 , MSP430F67671A , MSP430F6767A , MSP430F6768 , MSP430F67681 , MSP430F67681A , MSP430F6768A , MSP430F6769 , MSP430F67691 , MSP430F67691A , MSP430F6769A , MSP430F6775 , MSP430F67751 , MSP430F67751A , MSP430F6775A , MSP430F6776 , MSP430F67761 , MSP430F67761A , MSP430F6776A , MSP430F6777 , MSP430F67771 , MSP430F67771A , MSP430F6777A , MSP430F6778 , MSP430F67781 , MSP430F67781A , MSP430F6778A , MSP430F6779 , MSP430F67791 , MSP430F67791A , MSP430F6779A , MSP430FE423 , MSP430FE4232 , MSP430FE423A , MSP430FE4242 , MSP430FE425 , MSP430FE4252 , MSP430FE425A , MSP430FE427 , MSP430FE4272 , MSP430FE427A , MSP430FG4250 , MSP430FG4260 , MSP430FG4270 , MSP430FG437 , MSP430FG438 , MSP430FG439 , MSP430FG4616 , MSP430FG4617 , MSP430FG4618 , MSP430FG4619 , MSP430FG477 , MSP430FG478 , MSP430FG479 , MSP430FG6425 , MSP430FG6426 , MSP430FG6625 , MSP430FG6626 , MSP430FR4131 , MSP430FR4132 , MSP430FR4133 , MSP430FR5870 , MSP430FR5872 , MSP430FR58721 , MSP430FR5922 , MSP430FR59221 , MSP430FR5970 , MSP430FR5972 , MSP430FR59721 , 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 , MSP430FW423 , MSP430FW425 , MSP430FW427 , MSP430FW428 , MSP430FW429

 

  1.   Designing With MSP430™ MCUs and Segment LCDs
    1.     Trademarks
    2. 1 Introduction: MSP430 + LCD End Applications
    3. 2 MSP430 LCD Portfolio
    4. 3 Segmented LCD Operation
      1. 3.1 LCD Structure (Simplified)
      2. 3.2 LCD Drive Basics
    5. 4 MSP430 LCD Features
      1. 4.1  Muxing
        1. 4.1.1 Muxing Example
      2. 4.2  Charge Pump
      3. 4.3  Biasing
      4. 4.4  Contrast Control
      5. 4.5  Timing
      6. 4.6  Memory Map
      7. 4.7  Blinking
      8. 4.8  LCD Output Pins
      9. 4.9  Ultra-Low-Power Features
      10. 4.10 Driving Large LCDs
    6. 5 LCD Layout and Software Considerations
      1. 5.1 LCD Layout Tips
        1. 5.1.1 Hardware-Driven Layout
        2. 5.1.2 Software-Driven Layout
        3. 5.1.3 General Layout Rules
      2. 5.2 LCD Software Tips
        1. 5.2.1 Create a Lookup Table
        2. 5.2.2 Use of #defines
        3. 5.2.3 Efficient Clearing of the LCD Memory
        4. 5.2.4 Double-Buffering of the Display Buffer Using Dual Display Memory
        5. 5.2.5 Efficient Binary-to-BCD Conversion
    7. 6 Devices Without LCD Module
      1. 6.1 Bit-Banged LCD
        1. 6.1.1 Bit-Banged LCD Tradeoffs
      2. 6.2 Displays With Built-in Drivers and Serial Interface
    8. 7 Additional Resources
  2.   Revision History

6.1.1 Bit-Banged LCD Tradeoffs

The 1/2 bias using this method is achieved by using resistor pairs and setting the pin as an input to generate the VCC/2 state. This consumes more current than using the LCD module to drive the display, because GPIOs consume more current when held near the switching point (this is why floating pins can consume excess current). With a built-in LCD module function, the LCD pins are designed and configured for analog function so they do not incur this penalty.

In addition, the signals are being set manually by software using a timer module to do the frame timing. In the example software for the app note, a 4-mux display is driven via GPIO. Since LCD signals cannot apply a DC level to the segment, the GPIO have to toggle within each portion of the frame. So in the example the timer must wake the device 8 times in each frame to set the GPIO – there are 4 time slots because it is a 4-mux display, but the device must wake twice for each time slot to toggle the pins so that no DC voltage is applied across the time slot. The device must do these operations 8 times per frame to maintain a constant image on the display, even when nothing on the display is changing. This means that this method has much more software overhead than using the LCD module, which can maintain the display image without CPU intervention, with software only needed when the display image should change. The additional software overhead can affect overall system throughput, can block or delay other interrupts in the system, and also means the device has to be awake for a larger percentage of the time leading to higher current consumption.

Therefore, this method should only be used for applications where these tradeoffs have been carefully considered – some applications are simple and can function adequately with this method, but for others this is too computationally intensive, consumes too much power, or a more complex display is required than this method can support.