Motorola ColdFire MCF5281 User Manual
Page 563
Queued Analog-to-Digital Converter (QADC)
Freescale Semiconductor
28-25
7
6
5
4
3
2
1
0
Field
IST1
IST0
CHAN5
CHAN4
CHAN3
CHAN2
CHAN1
CHAN0
Reset
Undefined
R/W:
R
Address
IPSBAR + 0x19_0200, 0x19_027e
Figure 28-14. Conversion Command Word Table (CCW)
Table 28-14. CCW Field Descriptions
Bit(s)
Name
Description
15–10
—
Reserved, should be cleared.
9
P
Pause. Allows subqueues to be created within queue 1 and queue 2. The QADC
performs the conversion specified by the CCW with the pause bit set and then the
queue enters the pause state. Another trigger event causes execution to continue from
the pause to the next CCW.
1 Enter pause state after execution of current CCW.
0 Do not enter pause state after execution of current CCW.
NOTE: The P bit does not cause the queue to pause in software-initiated modes or
externally gated modes.
8
BYP
Sample amplifier bypass. Enables the amplifier bypass mode for a conversion and
subsequently changes the timing. The initial sample time is eliminated, reducing the
potential conversion time by two QCLKs. However, due to internal RC effects, a
minimum final sample time of four QCLKs must be allowed. When using this mode,
the external circuit should be of low source impedance. Loading effects of the external
circuitry need to be considered because the benefits of the sample amplifier are not
present.
1 Amplifier bypass mode enabled
0 Amplifier bypass mode disabled
NOTE: BYP is maintained for software compatibility but has no functional benefit on
this version of the QADC.
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.
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.
shows the channel number assignments for non-multiplexed mode.
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.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3