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ST63156 数据表(PDF) 27 Page - STMicroelectronics |
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ST63156 数据表(HTML) 27 Page - STMicroelectronics |
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27 / 86 page ![]() Instruction Type Cycles Execution Time Branch if set/reset 5 Cycles 8.125 µs Branch & Subroutine Branch 4 Cycles 6.50 µs Bit Manipulation 4 Cycles 6.50 µs Load Instruction 4 Cycles 6.50 µs Arithmetic & Logic 4 Cycles 6.50 µs Conditional Branch 2 Cycles 3.25 µs Program Control 2 Cycles 3.25 µs Table 7. Intructions Timing with 8MHz Clock Figure 23. Clock Generator Option (1) Figure 24. Clock Generator Option (2) Figure 25. OSCin, OSCout Diagram The internal oscillator circuit is designed to require a minimum of external components. A crystal quartz, a ceramic resonator, or an external signal (provided to the OSCin pin) may be used to gener- ate a system clock with various stability/cost trade- offs. The typical clock frequency is 8MHz. Please note that different frequencies will affect the opera- tion of those peripherals (D/As, SPI, 62.5 kHz OUT) whose reference frequencies are derived from the system clock. The different clock generator options connection methods are shown in Figures 24 and 25. One ma- chine cycle takes 13 oscillator pulses; 12 clock pulses are needed to increment the PC while and additional 13th pulse is needed to stabilize the in- ternal latches during memory addressing. This means that with a clock frequency of 8MHz the ma- chine cycle is 1.625 µSec. The crystal oscillator start-up time is a function of many variables: crystal parameters (especially RS), oscillator load capacitance (CL), IC parame- ters, ambient temperature, and supply voltage.It must be observed that the crystal or ceramic leads and circuit connections must be as short as possi- ble. Typical values for CL1 and CL2 are in the range of 15pF to 22pF but these should be chosen based on the crystal manufacturers specification. Typical input capacitance for OSCin and OSCout pins is 5pF. The oscillator output frequency is internallydivided by 13 to produce the machine cycle and by 12 to produce the Timer and the Watchdog clock. A byte cycle is the smallest unit needed to execute any operation (i.e., increment the program counter). An instruction may need two, four, or five byte cycles to be executed (See Table 7). ON-CHIP CLOCK OSCILLATOR ® ST63140,142,126,156 23/82 |
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