MPC555
/
MPC556
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
13-26
Figure 13-8 QADC64 Clock Subsystem Functions
To accommodate wide variations of the main MCU clock frequency (IMB clock —
F
SYS
), QCLK is generated by a programmable prescaler which divides the MCU IMB
clock to a frequency within the specified QCLK tolerance range. To allow the A/D con-
version time to be maximized across the spectrum of IMB clock frequencies, the
QADC64 prescaler permits the frequency of QCLK to be software selectable. It also
allows the duty cycle of the QCLK waveform to be programmable.
The software establishes the basic high phase of the QCLK waveform with the PSH
(prescaler clock high time) field in QACR0, and selects the basic low phase of QCLK
with the prescaler clock low time (PSL) field. The combination of the PSH and PSL pa-
rameters establishes the frequency of the QCLK.
PRESCALER RATE SELECTION
(FROM CONTROL REGISTER 0):
BINARY COUNTER
PERIODIC/INTERVAL
TIMER SELECT
215
214
213
212
211
210
29
28
27
216 217
ONE'S COMPLEMENT
COMPARE
CLOCK
GENERATE
5-BIT
DOWN COUNTER
ZERO
DETECT
RESET QCLK
LOAD PSH
SET QCLK
QCLK
QADC64 CLOCK
( F
SYS
/ ÷2 TO F
SYS
/÷40 )
LOW TIME CYCLES (PSL)
ADD HALF CYCLE TO HIGH (PSA)
HIGH TIME CYCLES (PSH)
INPUT SAMPLE TIME (FROM CCW)
Queue 1 & 2 TIMER MODE RATE SELECTION
SAR CONTROL
SAR
PERIODIC/INTERVAL
TRIGGER EVENT
5
3
3
2
5
IMB CLOCK (F
SYS
)
A/D CONVERTER
STATE MACHINE
FOR Q1 AND Q2
2
8
10
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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