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Register Descriptions
Bit(s)
Name
7–6
IST
5–0
CHAN
Table 27-16. Non-Multiplexed Channel Assignments and Signal Designations
Port Signal Name
PQB0
PQB1
PQB2
PQB3
PQA0
PQA1
PQA3
PQA4
V
RL
V
RH
—
—
1
All channels not listed are reserved or unimplemented and return undefined results.
27-28
Table 27-14. CCW Field Descriptions (continued)
Input sample time. Specifies the length of the sample window. The input sample time can be
varied, under software control, to accommodate various input channel source impedances.
Longer sample times permit more accurate A/D conversions of signals with higher source
impedances.
Table 27-15 shows the four selectable input sample times.
The programmable sample time can also be used to adjust queue execution time or sampling
rate by increasing the time interval between conversions.
Selects the input channel number. The CCW channel field is programmed with the channel
number corresponding to the analog input signal to be sampled and converted. The analog input
signal channel number assignments and the signal definitions vary depending on whether the
QADC multiplexed or non-multiplexed mode is used by the application. As far as queue
scanning operations are concerned, there is no distinction between an internally or externally
multiplexed analog input.
Table 27-16 shows the channel number assignments for non-multiplexed mode. Table 27-17
shows the channel number assignments for multiplexed mode.
Programming the channel field to channel 63 denotes the end of the queue. Channels 60 to 62
are special internal channels. When one of the special channels is selected, the sampling
amplifier is not used. The value of V
Programming any input sample time other than two has no benefit for the special internal
channels except to lengthen the overall conversion time.
Table 27-15. Input Sample Times
IST[1:0]
Input sample time = QCLK period × 2
00
Input sample time = QCLK period × 4
01
Input sample time = QCLK period × 8
10
Input sample time = QCLK period × 16
11
Non-Multiplexed Input Signals
Analog Signal Name
AN0
AN1
AN2
AN3
AN52
AN53
AN55
AN56
Low reference
High reference
—
—
MCF5282 User's Manual
Description
, V
, or (V
RL
RH
Input Sample Times
Other
Functions
—
—
—
—
—
—
ETRIG1
ETRIG2
—
—
(V
–V
)/2
RH
RL
End-of-Queue Code
–V
)/2 is converted directly.
RH
RL
Channel Number
in CCW CHAN Field
Signal Type
Binary
Input
000000
Input
000001
Input
000010
Input
000011
Input/Output
110100
Input/Output
110101
Input/Output
110111
Input/Output
111000
Input
111100
Input
111101
—
111110
—
111111
1
Decimal
0
1
2
3
52
53
55
56
60
61
62
63
MOTOROLA
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