MPC555
/
MPC556
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
13-12
Figure 13-4 QADC64 Module Block Diagram
13.9.1 Conversion Cycle Times
Total conversion time is made up of initial sample time, final sample time, and resolu-
tion time. Initial sample time refers to the time during which the selected input channel
is driven by the buffer amplifier onto the sample capacitor. The buffer amplifier can be
disabled by means of the BYP bit in the CCW. During the final sampling period, ampli-
fier is bypassed, and the multiplexer input charges the RC DAC array directly. During
the resolution period, the voltage in the RC DAC array is converted to a digital value
and stored in the SAR.
Initial sample time is fixed at two QCLK cycles. Final sample time can be 2, 4, 8, or 16
QCLK cycles, depending on the value of the IST field in the CCW. Resolution time is
ten QCLK cycles.
Sample and resolution require a minimum of 14 QCLK clocks (7
µ
s with a 2-MHz
QCLK). If the maximum final sample time period of 16 QCLKs is selected, the total
conversion time is 13.0
µ
s with a 2-MHz QCLK.
illustrates the timing for conversions. This diagram assumes a final
sampling period of two QCLK cycles.
PQA7
PQA0
PQB7
PQB0
CHAN. DECODE & MUX
VDDA
VSSA
16: 1
VRH
VRL
QADC64 DETAIL BLOCK
QCLK
WCCW
END OF CONV.
RST
STOP
SAR
10 BIT A/D CONVERTER
INPUT
ANALOG
POWER
RSAR
SAMPLE
COMPAR-
SUCCESSIVE
ATOR
BIAS CIRCUIT
APPROXIMATION
REGISTER
BUFFER
STATE MACHINE & LOGIC
10
10
CCW
6
POWER
DOWN
SIG
NAL
S F
R
OM
/T
O
Q
U
E
U
E CONT
ROL
L
O
GIC
SAR Timing
10 BIT RC
DAC
CSAMP
CHAN.[5:0]
SAR
BUF
CCW
BUF
END OF SMP
10
10
IS
T
BY
P
2
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..