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HT1621 データシート(PDF) 11 Page - Holtek Semiconductor Inc |
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HT1621 データシート(HTML) 11 Page - Holtek Semiconductor Inc |
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11 / 20 page  HT1621 11 April 21, 2000 TIMER command. The CLR WDT or the CLR TIMER command should be executed prior to the WDT EN or the TIMER EN command re- spectively. Before executing the IRQ EN com- mand the CLR WDT or CLR TIMER command should be executed first. The CLR TIMER com- mand has to be executed before switching from the WDT mode to the time base mode. Once the WDT time-out occurs, the IRQ pin will stay at a logic low level until the CLR WDT or the IRQ DIS command is issued. After the IRQ output is disabled the IRQ pin will remain at the floating state. The IRQ output can be enabled or dis- abled by executing the IRQ EN or the IRQ DIS command, respectively. The IRQ EN makes the output of the time base generator or of the WDT time-out flag appear on the IRQ pin. The config- uration of the time base generator along with the WDT are as shown. In the case of on-chip RC oscillator or crystal oscillator, the power down mode can reduce power consumption since the oscillator can be turned on or off by the corresponding system commands. At the power down mode the time base/WDT loses all its functions. On the other hand, if an external clock is se- lected as the source of system frequency the SYS DIS command turns out invalid and the power down mode fails to be carried out. That is, after the external clock source is selected, the HT1621 will continue working until system power fails or the external clock source is re- moved. After the system power on, the IRQ will be disabled. Tone output A simple tone generator is implemented in the HT1621. The tone generator can output a pair of differential driving signals on the BZ and BZ, which are used to generate a single tone. By ex- ecuting the TONE4K and TONE2K commands there are two tone frequency outputs selectable. The TONE4K and TONE2K com- mands set the tone frequency to 4kHz and 2kHz, respectively. The tone output can be turned on or off by invoking the TONE ON or the TONE OFF command. The tone outputs, namely BZ and BZ, are a pair of differential driving outputs used to drive a piezo buzzer. Once the system is disabled or the tone output is inhibited, the BZ and the BZ outputs will re- main at low level. LCD driver The HT1621 is a 128 (32´4) pattern LCD driver. It can be configured as 1/2 or 1/3 bias and 2 or 3 or 4 commons of LCD driver by the S/W configu- ration. This feature makes the HT1621 suitable for multiply LCD applications. The LCD driving clock is derived from the system clock. The value of the driving clock is always 256Hz even when it is at a 32.768kHz crystal oscillator frequency, an on-chip RC oscillator frequency, or an external frequency. The LCD corresponding commands are summarized in the table. The bold form of100, namely 100, indicates the command mode ID. If successive commands have been issued, the command mode ID except for the first command, will be omitted. The LCD Name Command Code Function LCD OFF 100 00000010X Turn off LCD outputs LCD ON 100 00000011X Turn on LCD outputs BIAS & COM 100 0010abXcX c=0: 1/2 bias option c=1: 1/3 bias option ab=00: 2 commons option ab=01: 3 commons option ab=10: 4 commons option |
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