參數(shù)資料
型號: QADCRM
英文描述: Queued Analog-to-Digital Converter Reference Manual
中文描述: 排隊模擬到數(shù)字轉(zhuǎn)換器參考手冊
文件頁數(shù): 58/122頁
文件大?。?/td> 940K
代理商: QADCRM
MOTOROLA
7-12
DIGITAL CONTROL
QADC
REFERENCE MANUAL
9. Code the selected PSH, PSL, and PSA values into the prescaler fields of
QACR0.
Figure 7-3
and
Table 7-1
show examples of QCLK programmability. The examples
include conversion times based on the following assumptions:
System clock (F
) = 20.97 MHz.
Input sample time is as fast as possible (IST = 0, 2 QCLK cycles).
Figure 7-3
and
Table 7-1
also show the conversion time calculated for a single con-
version in a queue. For other MCU system clock frequencies and other input sample
times, the same calculations can be made.
Figure 7-3 QADC Clock Programmability Examples
The MCU system clock frequency is the basis of the QADC timing. The QADC requires
that the system clock frequency be at least twice the QCLK frequency. Refer to
AP-
PENDIX A ELECTRICAL CHARACTERISTICS
for information on the minimum and
maximum allowable QCLK frequencies.
The QCLK frequency is established by the combination of the PSH and PSL parame-
ters in QACR0. The 5-bit PSH field selects the number of system clock cycles in the
high phase of the QCLK wave. The 3-bit PSL field selects the number of system clock
cycles in the low phase of the QCLK wave.
Example 1 in
Figure 7-3
shows that when PSH = 3, the QCLK remains high for four
cycles of the system clock. It also shows that when PSL = 3, the QCLK remains low
for four system clock cycles. In example 1, the equation for QCLK high cycles is the
PSH value plus one, and the equation for the QCLK low cycles is the PSL value plus
one.
Table 7-1 QADC Clock Programmability
Control Register 0 Information
F
SYS
= 20.97
Input Sample Time (IST) = %00
QCLK
(MHz)
1.0
1.0
Example
Number
1
2
PSH
PSA
PSL
Conversion Time
(
μ
s)
18.0
18.0
7
7
0
1
7
7
QCLK EXAMPLES
F
SYS
EX1
EX2
SYSTEM CLOCK
QADC QCLK EX
16 CYCLES
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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