参数资料
型号: MC68HC05V7CB
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDIP56
封装: SDIP-56
文件页数: 148/170页
文件大小: 980K
代理商: MC68HC05V7CB
SECTION 10: A/D CONVERTER
MOTOROLA
Page 65
MC68HC05V7 Specification Rev. 1.0
SECTION 10
A/D CONVERTER
The MC68HC705V7 includes a 16 channel, 8-bit, multiplexed input, successive
approximation A/D converter. When the device is packaged (in a 56-pin SDIP), pin number
restrictions require that 8 channels, AN8 through AN15, are not bonded out.
10.1
ANALOG SECTION
10.1.1
RATIOMETRIC CONVERSION
The A/D is ratiometric, with two dedicated pins supplying the reference voltages (V
REFH
and V
REFL
)
. An input voltage equal to V
REFH converts to $FF (full scale) and an input
voltage equal to V
REFL converts to $00. An input voltage greater than VREFH will convert
to $FF with no overflow indication. For ratiometric conversions, the source of each analog
input should use V
REFH as the supply voltage and be referenced to VREFL.
10.1.2
V
REFH AND VREFL
The reference supply for the converter uses two dedicated pins rather than being driven by
the system power supply lines because the voltage drops in the bonding wires of those
heavily loaded pins would degrade the accuracy of the A/D conversion. V
REFH and VREFL
can be any voltage between V
SSA1 and VCCA, as long as VREFH > VREFL; however, the
accuracy of conversions is tested and guaranteed only for V
REFL = VSSA1
and V
REFH = VCCA.
10.1.3
ACCURACY AND PRECISION
The 8-bit conversions shall be accurate to within
± 1 1/2 LSB including quantization.
10.2
CONVERSION PROCESS
The A/D reference inputs are applied to a precision internal digital-to-analog converter.
Control logic drives this D/A and the analog output is successively compared to the
selected analog input which was sampled at the beginning of the conversion time. The
conversion process is monotonic and has no missing codes.
10.3
DIGITAL SECTION
10.3.1
CONVERSION TIMES
Each channel of conversion takes 32 clock cycles, which must be at a frequency equal to
or greater than 1 MHz.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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