Rev. 1.00
44
September 11, 2018
Rev. 1.00
45
September 11, 2018
HT45F4050
A/D NFC Flash MCU
HT45F4050
A/D NFC Flash MCU
Note: 1. R
P
, C1 and C2 are required.
2. Although not shown XT1/XT2 pins have a parasitic
capacitance of around 7pF.
To internal
circuits
Internal
Oscillator
Circuit
C1
C2
XT1
XT2
R
P
32.768
kHz
Internal RC
Oscillator
External LXT Oscillator
LXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
32.768kHz
10pF
10pF
Note: 1. C1 and C2 values are for guidance only.
2. R
P
=5M~10MΩ is recommended.
32.768kHz Crystal Recommended Capacitor Values
Internal 32kHz Oscillator – LIRC
The Internal 32
kHz System Oscillator is one of the low frequency oscillator choices, which is
selected via a software control bit, FSS. It is a fully integrated RC oscillator with a typical frequency
of 32kHz at full voltage range, requiring no external components for its implementation. 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.
Operating Modes and System Clocks
Present day applications require that their microcontrollers have high performance but often still
demand that they consume as little power as possible, conflicting requirements that are especially
true in battery powered portable applications. The fast clocks required for high performance will
by their nature increase current consumption and of course vice-versa, lower speed clocks reduce
current consumption. As Holtek has provided the device with both high and low speed clock sources
and the means to switch between them dynamically, the user can optimise the operation of their
microcontroller to achieve the best performance/power ratio.
System Clocks
The device has different clock sources for both the CPU and peripheral function operation. By
providing the user with a wide range of clock selections using register programming, a clock system
can be configured to obtain maximum application performance.
The main system clock, can come from either a high frequency, f
H
, or low frequency, f
SUB
, source, and is
selected using the CKS2~CKS0 bits in the SCC register. The high speed system clock is sourced from an
HXT or HIRC oscillator, selected via configuring the FHS bit in the SCC register. The low speed system
clock source can be sourced from the internal clock f
SUB
. If f
SUB
is selected then it can be sourced by
either the LXT or LIRC oscillators, selected via configuring the FSS bit in the SCC register. The other
choice, which is a divided version of the high speed system oscillator has a range of f
H
/2~f
H
/64.