HT46R068B Datasheet, PDF (35/134 Pages) Holtek Semiconductor Inc – Enhanced A/D Type 8-bit OTP MCU

HT46R068B/HT46R069B
Enhanced A/D Type 8-bit OTP MCU
Internal RC Oscillator – HIRC
The internal RC oscillator is a fully integrated system oscillator requiring no external components.
The internal RC oscillator has three fixed frequencies of either 4MHz, 8MHz or 12MHz. Device
trimming during the manufacturing process and the inclusion of internal frequency compensation
circuits are used to ensure that the influence of the power supply voltage, temperature and process
variations on the oscillation frequency are minimised. As a result, at a power supply of either 3V or
5V and at a temperature of 25 degrees, the fixed oscillation frequency of 4MHz, 8MHz or 12MHz
will have a tolerance within 2%. Note that if this internal system clock option is selected, as it
requires no external pins for its operation, I/O pins PA5 and PA6 are free for use as normal I/O pins.
P A 5 /O S C 2
P A 6 /O S C 1
In te rn a l R C
O s c illa to r
N o te : P A 5 /P A 6 u s e d a s n o rm a l I/O s
Internal RC Oscillator — HIRC
External 32768Hz Crystal Oscillator – LXT
The LXT oscillator is used both as the slow system clock and also as a selectable source clock for
some peripheral functions including the Watchdog Timer, Time Base, Timer/Event Counters and
SPI functions. It must be first enabled using a configuration option.
To select the LXT oscillator to be the low speed system oscillator, the CLKMOD bit in the CTRL0
register should be set high. When a HALT instruction is executed, the system clock is stopped, but
the LXTEN bit in the CTRL2 register determines if the LXT oscillator continues running when the
microcontroller powers down. Setting the LXTEN bit high will enable the LXT to keep running
after a HALT instruction is executed and enable the LXT oscillator to remain as a possible clock
source for the Watchdog Timer, the Time-Base and the Timer/Event Counter 0/1.
The LXT oscillator is implemented using a 32768Hz crystal connected to pins XT1/XT2.
However, for some crystals and to ensure oscillation and accurate frequency generation, it is
normally necessary to add two small value external capacitors, C1 and C2. The exact values of C1
and C2 should be selected in consultation with the crystal or resonator manufacturer specification.
The external parallel feedback resistor, Rp, may also be required.
Rev. 1.00
30
January 26, 2011