5.1.2 Software-Driven Layout

Using a software-driven approach for pin selection and layout would choose to connect LCD segment pins on the LCD display to groups of LCD Sx pins on the MSP430 MCU that map adjacent areas in the LCD memory. This allows the MSP430 to set all required segments to display digits/characters using a single memory write of a byte or word. For example, for the 4-mux display shown previously in Figure 13, 2 pins control all the segments to display any digit 0-9, and 4 pins control all the segments to display any alphanumeric character. In 4-mux mode, the MSP430 LCD memory has each byte controlling 2 Sx pins. Therefore, with careful connections between the MSP430 and this LCD glass, a full digit could be set on the display with a single byte access (writing 2 pins at once), or a full alphabet character could be set on the display with a single word access (writing 4 pins at once). Figure 15 shows an example of choosing MSP430 Sx pins within the same LCDMx memory register so that all segments for both Sx pins can be set with a single byte access. It is also important to make sure that the same segments for each digit are assigned to the same ordering within the byte and are laid out in the same format in memory – this ensures that the same function call can be used no matter which digit of the display you are trying to set, saving greatly on software overhead.

However doing the layout for these connections may also be more complex depending on the application, or require a multi-layered board. On devices with the LCD_E module, any pin can be a COM pin or a segment pin helping to make layout easier, so this can help to mitigate this problem to an extent.