Motorola MCF5281 사용자 설명서
27-28
MCF5282 User’s Manual
MOTOROLA
Register Descriptions
7–6
IST
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.
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.
5–0
CHAN
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
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
RL
, V
RH
, or (V
RH
–V
RL
)/2 is converted directly.
Programming any input sample time other than two has no benefit for the special internal
channels except to lengthen the overall conversion time.
channels except to lengthen the overall conversion time.
Table 27-15. Input Sample Times
IST[1:0]
Input Sample Times
00
Input sample time = QCLK period
× 2
01
Input sample time = QCLK period
× 4
10
Input sample time = QCLK period
× 8
11
Input sample time = QCLK period
× 16
Table 27-16. Non-Multiplexed Channel Assignments and Signal Designations
Non-Multiplexed Input Signals
Channel Number
1
in CCW CHAN Field
1
All channels not listed are reserved or unimplemented and return undefined results.
Port Signal Name
Analog Signal Name
Other
Functions
Signal Type
Binary
Decimal
PQB0
PQB1
PQB2
PQB3
PQB1
PQB2
PQB3
AN0
AN1
AN2
AN3
AN1
AN2
AN3
—
—
—
—
—
—
—
Input
Input
Input
Input
Input
Input
Input
000000
000001
000010
000011
000001
000010
000011
0
1
2
3
1
2
3
PQA0
PQA1
PQA1
AN52
AN53
AN53
—
—
—
Input/Output
Input/Output
Input/Output
110100
110101
110101
52
53
53
PQA3
PQA4
PQA4
AN55
AN56
AN56
ETRIG1
ETRIG2
ETRIG2
Input/Output
Input/Output
Input/Output
110111
111000
111000
55
56
56
V
RL
V
RH
—
Low reference
High reference
—
—
—
—
(V
RH
–V
RL
)/2
Input
Input
Input
—
111100
111101
111110
111101
111110
60
61
62
61
62
—
—
End-of-Queue Code
—
111111
63
Table 27-14. CCW Field Descriptions (continued)
Bit(s)
Name
Description