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MCP2515-I/ST 参数 Datasheet PDF下载

MCP2515-I/ST图片预览
型号: MCP2515-I/ST
PDF下载: 下载PDF文件 查看货源
内容描述: 独立CAN控制器,SPI ™接口 [Stand-Alone CAN Controller With SPI⑩ Interface]
分类和应用: 控制器
文件页数/大小: 84 页 / 993 K
品牌: MICROCHIP [ MICROCHIP ]
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MCP2515  
8.2  
CLKOUT Pin  
8.0  
OSCILLATOR  
The CLKOUT pin is provided to the system designer for  
use as the main system clock or as a clock input for  
other devices in the system. The CLKOUT has an inter-  
nal prescaler which can divide FOSC by 1, 2, 4 and 8.  
The CLKOUT function is enabled and the prescaler is  
selected via the CANCNTRL register (see  
Register 10-1).  
The MCP2515 is designed to be operated with a crystal  
or ceramic resonator connected to the OSC1 and  
OSC2 pins. The MCP2515 oscillator design requires  
the use of a parallel cut crystal. Use of a series cut  
crystal may give a frequency out of the crystal  
manufacturers specifications. A typical oscillator circuit  
is shown in Figure 8-1. The MCP2515 may also be  
driven by an external clock source connected to the  
OSC1 pin, as shown in Figure 8-2 and Figure 8-3.  
Note:  
The maximum frequency on CLKOUT is  
specified as 25 MHz (See Table 13-5)  
The CLKOUT pin will be active upon system reset and  
default to the slowest speed (divide by 8) so that it can  
be used as the MCU clock.  
8.1  
Oscillator Startup Timer  
The MCP2515 utilizes an Oscillator Startup Timer  
(OST) that holds the MCP2515 in reset to ensure that  
the oscillator has stabilized before the internal state  
machine begins to operate. The OST maintains reset  
for the first 128 OSC1 clock cycles after power-up or a  
wake-up from Sleep mode occurs. It should be noted  
that no SPI protocol operations should be attempted  
until after the OST has expired.  
When Sleep mode is requested, the MCP2515 will  
drive sixteen additional clock cycles on the CLKOUT  
pin before entering Sleep mode. The idle state of the  
CLKOUT pin in Sleep mode is low. When the CLKOUT  
function is disabled (CANCNTRL.CLKEN = ‘0’) the  
CLKOUT pin is in a high-impedance state.  
The CLKOUT function is designed to ensure that  
thCLKOUT and tlCLKOUT timings are preserved when the  
CLKOUT pin function is enabled, disabled or the  
prescaler value is changed.  
FIGURE 8-1:  
CRYSTAL/CERAMIC RESONATOR OPERATION  
OSC1  
C1  
To internal logic  
SLEEP  
XTAL  
(2)  
RF  
(1)  
RS  
C2  
OSC2  
Note 1: A series resistor (RS) may be required for AT strip cut crystals.  
2: The feedback resistor (RF), is typically in the range of 2 to 10 MΩ.  
FIGURE 8-2:  
EXTERNAL CLOCK SOURCE  
Clock from  
OSC1  
external system  
(1)  
OSC2  
Open  
Note 1: A resistor to ground may be used to reduce system noise. This may increase system current.  
2: Duty cycle restrictions must be observed (see Table 12-2).  
© 2005 Microchip Technology Inc.  
Preliminary  
DS21801D-page 53  
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