LCD_F Controller Architecture and Operation
997
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
LCD_F Controller
27.2 LCD_F Controller Architecture and Operation
27.2.1 Power Management
27.2.1.1 General Considerations
The LCD controller is fully operational in active, LPM0, LF_AM, and LF_LPM0 device power modes.
Partial operation is supported in LPM3. The controller is off in LPM3.5, LPM4, and LPM4.5.
27.2.1.1.1 Operation in LPM3
In LPM3, register writes and memory access are not possible. However, if the LCD controller is kept
operational (LCDON = 1) before entering LPM3, the LCD controller continues to drive the display with the
last written pattern while in LPM3. Animation and blink features are also available in LPM if programmed
before entering LPM3.
27.2.2 Clock System
27.2.2.1 LCD Timing Generation
The LCD_F controller uses the f
LCD
signal from the integrated clock divider to generate the timing for
common and segment lines. The LCDSSEL bits select from the following as the clock source into the
divider: ACLK with a frequency between 10 kHz and 128 kHz, VLOCLK, REFOCLK, or LFXTCLK. The f
LCD
frequency is set by the LCDPREx and LCDDIVx bits. The resulting f
LCD
frequency is calculated by
.
(14)
The proper f
LCD
frequency depends on the LCD's requirement for framing frequency and the LCD multiplex
rate. It is calculated by
.
f
LCD
= 2 × mux × f
Frame
(15)
For example, to calculate f
LCD
for a 3-mux LCD with a frame frequency of 30 Hz to 100 Hz:
f
Frame
(from LCD data sheet) = 30 Hz to 100 Hz
f
LCD
= 2 × 3 × f
Frame
f
LCD
(min) = 180 Hz
f
LCD
(max) = 600 Hz
With f
ACLK/VLOCLK/REFOCLK/LFXTCLK
= 32768 Hz, LCDPREx = 011, and LCDDIVx = 10101:
f
LCD
= 32768 Hz / ((21+1) × 2
3
) = 32768 Hz / 176 = 186 Hz
With LCDPREx = 001 and LCDDIVx = 11011:
f
LCD
= 32768 Hz / ((27+1) × 2
1
) = 32768 Hz / 56 = 585 Hz
The lowest frequency has the lowest current consumption. The highest frequency has the least flicker.
27.2.3 Interrupts
27.2.3.1 General Considerations
The LCD_F module has five interrupt sources, each with independent enables (LCDIE register) and flags
(LCDIFG register).
The five interrupt flags are LCDBLKONIFG, LCDBLKOFFIFG, LCDFRMIFG, LCDANMSTPIFG,
LCDANMLOOPIFG and can be independently triggered by hardware, and also, set (LCDSETIFG register)
and cleared (LCDCLRIFG register) by software.
•
LCDBLKONIFG is set at the BLKCLK edge synchronized to the frame boundaries that blanks the
segments when blinking is enabled with LCDBLKMODx = 01 or 10. It is also set at the BLKCLK edge
synchronized to the frame boundaries that selects the blinking memory as display memory when
LCDBLKMODx = 11. It is automatically cleared when a LCD or blinking memory register is written.