MC68336/376
REGISTER SUMMARY
MOTOROLA
USER’S MANUAL
D-37
D.5.8 Conversion Command Word Table
P — Pause
The pause bit allows the creation of sub-queues 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.
0 = Do not enter the pause state after execution of the current CCW.
1 = Enter the pause state after execution of the current CCW.
BYP — Sample Amplifier Bypass
Setting BYP enables the amplifier bypass mode for a conversion, and subsequently
for more information.
0 = Amplifier bypass mode disabled.
1 = Amplifier bypass mode enabled.
IST[1:0] — Input Sample Time
The IST field specifies the length of the sample window. Longer sample times permit
more accurate A/D conversions of signals with higher source impedances.
Table D-28 shows the bit encoding of the IST field.
CHAN[5:0] — Channel Number
The CHAN field selects the input channel number corresponding to the analog input
pin to be sampled and converted. The analog input pin channel number assignments
and the pin definitions vary depending on whether the QADC is operating in multi-
plexed or non-multiplexed mode. The queue scan mechanism sees no distinction be-
tween an internally or externally multiplexed analog input.
CHAN specifies a reserved channel number (channels 32 to 47) or an invalid channel
number (channels 4 to 31 in non-multiplexed mode), the low reference level (VRL) is
converted. Programming the channel field to channel 63 indicates the end of the
queue. Channels 60 to 62 are special internal channels. When one of these channels
is selected, the sample amplifier is not used. The value of VRL, VRH, or VDDA/2 is
placed directly onto the converter. Programming the input sample time to any value
other than two for one of the internal channels has no benefit except to lengthen the
overall conversion time.
CCW[0:27] — Conversion Command Word Table
$YFF230–$YFF27E
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
NOT USED
P
BYP
IST[1:0]
CHAN[5:0]
RESET:
U
Table D-28 Input Sample Times
IST[1:0]
Input Sample Times
00
2 QCLK periods
01
4 QCLK periods
10
8 QCLK periods
11
16 QCLK periods
336376UMBook Page 37 Friday, November 15, 1996 2:09 PM