欢迎访问ic37.com |
会员登录 免费注册
发布采购

68HC705JJ7_1 参数 Datasheet PDF下载

68HC705JJ7_1图片预览
型号: 68HC705JJ7_1
PDF下载: 下载PDF文件 查看货源
内容描述: 常规版本规格 [General Release Specification]
分类和应用:
文件页数/大小: 230 页 / 5548 K
品牌: FREESCALE [ Freescale ]
 浏览型号68HC705JJ7_1的Datasheet PDF文件第127页浏览型号68HC705JJ7_1的Datasheet PDF文件第128页浏览型号68HC705JJ7_1的Datasheet PDF文件第129页浏览型号68HC705JJ7_1的Datasheet PDF文件第130页浏览型号68HC705JJ7_1的Datasheet PDF文件第132页浏览型号68HC705JJ7_1的Datasheet PDF文件第133页浏览型号68HC705JJ7_1的Datasheet PDF文件第134页浏览型号68HC705JJ7_1的Datasheet PDF文件第135页  
Freescale Semiconductor, Inc.  
Analog Subsystem  
Voltage Measurement Methods  
8.7.2 Ra tiom e tric Volta g e Re a d ing s  
The ratiometric value of a voltage measurement can be calculated in  
software by first taking a reference reading from a reference source and  
then comparing subsequent unknown voltages to that reading as a  
percentage of the reference value. The accuracy of ratiometric readings  
will depend on the variety of sources, but will generally be better than for  
absolute readings. Many of these error sources can be taken into  
account using the features of the analog subsystem and appropriate  
software as described in Table 8-7. As with absolute measurements,  
most of the errors can be reduced by frequent comparisons to the  
reference voltage, use of the inverted comparator inputs, and averaging  
of multiple samples.  
8.7.2.1 Inte rna l Ra tio m e tric Re fe re nc e  
If readings are to be ratiometric to V , the reference measurement  
DD  
point can be internally selected. In this case the reference reading can  
be taken by setting the V  
bit and clearing the MUX1:4 bits in the  
REF  
AMUX register which connects the channel selection bus to the V pin.  
DD  
In order to stay within the V  
range the DHOLD bit should be used to  
MAX  
select the 1/2 divided input.  
8.7.2.2 Exte rna l Ra tio m e tric Re fe re nc e  
If readings are to be ratiometric to some external source, the reference  
measurement point can be connected to any one of the channel selected  
pins from PB1–PB4. In this case, the reference reading can be taken by  
setting the MUX bit in the AMUX which connects channel selection bus  
to the pin connected to the external reference source. If the external  
reference is greater than V –1.5 volts, then the DHOLD bit should be  
DD  
used to select the 1/2 divided input.  
MC68HC705JJ7/MC68HC705JP7 Rev. 3.0  
General Release Specification  
Analog Subsystem  
For More Information On This Product,  
Go to: www.freescale.com  
 复制成功!