MPC555
/
MPC556
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
13-28
FQCLK = 1/(250 + 250) = 2 MHz
and
show examples of QCLK programmability. The examples
include conversion times based on the following assumption:
• Input sample time is as fast as possible (IST = 0, 2 QCLK cycles).
and
also show the conversion time calculated for a single con-
version in a queue. For other MCU IMB clock frequencies and other input sample
times, the same calculations can be made.
Figure 13-9 QADC64 Clock Programmability Examples
NOTE
PSA is maintained for software compatibility but has no functional
benefit to this version of the module.
The MCU IMB clock frequency is the basis of the QADC64 timing. The QADC64 re-
quires that the IMB clock frequency be at least twice the QCLK frequency. The QCLK
frequency is established by the combination of the PSH and PSL parameters in
QACR0. The 5-bit PSH field selects the number of IMB clock cycles in the high phase
of the QCLK wave. The 3-bit PSL field selects the number of IMB clock cycles in the
low phase of the QCLK wave.
Example 1 in
shows that when PSH = 11, the QCLK remains high for
twelve cycles of the IMB clock. It also shows that when PSL = 7, the QCLK remains
low for eight IMB clock cycles. In Example 2, PSH = 7, the QCLK remains high for eight
Table 13-4 QADC64 Clock Programmability
Control Register 0 Information
Input Sample Time (IST) =%00
Example
Number
Frequency
PSH
PSA
PSL
QCLK
(MHz)
Conversion Time
(
µ
s)
1
40 MHz
11
0
7
2.0
7.0
2
32 MHz
7
0
7
2.0
7.0
QCLK EXAMPLES
F
SYS
40 MHz EX1
32 MHz EX2
IMB CLOCK
QADC64 QCLK EX
20 CYCLES
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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