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C8051F339 参数 Datasheet PDF下载

C8051F339图片预览
型号: C8051F339
PDF下载: 下载PDF文件 查看货源
内容描述: 混合信号ISP功能的Flash MCU系列 [Mixed Signal ISP Flash MCU Family]
分类和应用:
文件页数/大小: 234 页 / 3348 K
品牌: SILICON [ SILICON ]
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C8051F336/7/8/9  
25.3.5. 8-bit, 9-bit, 10-bit and 11-bit Pulse Width Modulator Modes  
Each module can be used independently to generate a pulse width modulated (PWM) output on its associ-  
ated CEXn pin. The frequency of the output is dependent on the timebase for the PCA counter/timer, and  
the setting of the PWM cycle length (8, 9, 10 or 11-bits). For backwards-compatibility with the 8-bit PWM  
mode available on other devices, the 8-bit PWM mode operates slightly different than 9, 10 and 11-bit  
PWM modes. It is important to note that all channels configured for 8/9/10/11-bit PWM mode will use  
the same cycle length. It is not possible to configure one channel for 8-bit PWM mode and another for 11-  
bit mode (for example). However, other PCA channels can be configured to Pin Capture, High-Speed Out-  
put, Software Timer, Frequency Output, or 16-bit PWM mode independently.  
25.3.5.1. 8-bit Pulse Width Modulator Mode  
The duty cycle of the PWM output signal in 8-bit PWM mode is varied using the module's PCA0CPLn cap-  
ture/compare register. When the value in the low byte of the PCA counter/timer (PCA0L) is equal to the  
value in PCA0CPLn, the output on the CEXn pin will be set. When the count value in PCA0L overflows, the  
CEXn output will be reset (see Figure 25.8). Also, when the counter/timer low byte (PCA0L) overflows from  
0xFF to 0x00, PCA0CPLn is reloaded automatically with the value stored in the module’s capture/compare  
high byte (PCA0CPHn) without software intervention. Setting the ECOMn and PWMn bits in the  
PCA0CPMn register, and setting the CLSEL bits in register PCA0PWM to 00b enables 8-Bit Pulse Width  
Modulator mode. If the MATn bit is set to ‘1’, the CCFn flag for the module will be set each time an 8-bit  
comparator match (rising edge) occurs. The COVF flag in PCA0PWM can be used to detect the overflow  
(falling edge), which will occur every 256 PCA clock cycles. The duty cycle for 8-Bit PWM Mode is given in  
Equation 25.2.  
Important Note About Capture/Compare Registers: When writing a 16-bit value to the PCA0 Cap-  
ture/Compare registers, the low byte should always be written first. Writing to PCA0CPLn clears the  
ECOMn bit to ‘0’; writing to PCA0CPHn sets ECOMn to ‘1’.  
(256 – PCA0CPHn)  
---------------------------------------------------  
Duty Cycle =  
256  
Equation 25.2. 8-Bit PWM Duty Cycle  
Using Equation 25.2, the largest duty cycle is 100% (PCA0CPHn = 0), and the smallest duty cycle is  
0.39% (PCA0CPHn = 0xFF). A 0% duty cycle may be generated by clearing the ECOMn bit to ‘0’.  
Rev. 0.2  
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