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AN2687 Datasheet(PDF) 13 Page - STMicroelectronics |
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AN2687 Datasheet(HTML) 13 Page - STMicroelectronics |
13 / 22 page AN2687 Example of a quadruplex LCD driver with STM8 Doc ID 14296 Rev 1 13/22 same interrupt function) and 2 Overflow events (OVF) in each phase. The latter are described below: ● During CCR1_1, VDD is applied to the segments that have to be turned on and 0, to the segments that have to be turned off. The COM line that corresponds to this phase is set to low level. Other COM lines are set to the VDD/2 level. ● During OVF1, all COM lines are inactive (set to low level), then if Vrms has to be decreased (see Figure 6) all segments are set low or, if it has to be increased (see Figure 7), all segments are set high. ● During CCR1_2, the segment lines are supplied with voltage levels that are inverted compared to those applied during CCR1_1. The COM line that corresponds to this phase is set to high level. Other COM lines are set to the VDD/2 level. ● During OVF2, if Vrms has to be decreased then all COM lines and segments are inactive (set to low level) and if Vrms has to be increased (see Figure 7), the COM lines are set high and the segments are set low. In order to reduce consumption, the MCU is placed in WFI (wait for interrupt) mode in the main routine. The MCU is then woken up by the Timer 2 interrupts and the external interrupts (PA4/PA5 connected to push-buttons, refer to Section 6 for more information). 3.2 Second method: Auto-wakeup In this method, the LCD timing is generated by the Auto-wakeup time base. The MCU is placed in Auto-wakeup mode, meaning that it is in Halt mode but woken up periodically as the LSI source clock (embedded low-power RC around 128 kHz) remains active. When woken up, the MCU toggles the COM and SEG lines in the AWU interrupt routine, exactly as it was doing in the previous method in the Timer 2 interrupt routine. The software contrast control is not as easy to implement with this method as AWU timeouts are fixed. It could be less fine-tuned. Using this method, consumption can be very low (a total consumption of 1.08 mA at 3.3 V with HSI as the master clock). |
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Descripción similar - AN2687 |
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