
MOTOROLA
Chapter 13. Queued Analog-To-Digital Converter (QADC64E)
13-31
Programming the QADC64E Registers
7
REF
Alternate Reference Enabled — Setting REF high in the CCW enables the use of an
alternate reference.
0 VRH is used as high reference
1 AltRef pin is used as the high reference
8
IST
Input Sample Time — The IST field allows software to specify the length of the sample
window. Provision is made to vary the input sample time, through software control, to offer
flexibility in the source impedance of the circuitry providing the QADC64E analog channel
inputs. Longer sample times permit more accurate A/D conversions of signals with higher
source impedances. The programmable sample time can also be used to increase the time
interval between conversions to adjust the queue execution time or the sampling rate.
Table 13-18 shows the two selectable input sample times.
9:15
CHAN[6:0]
CHAN[6:0] — Channel Number — The CHAN field selects the input channel number. The
software programs the channel field of the CCW with the 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 multiplexed or
non-multiplexed mode is used by the application. As far as the queue scanning operations
are concerned, there is no distinction between an internally or externally multiplexed analog
multiplexing.
Table 13-18. Input Sample Times
IST
Input Sample Times
0
Input sample time = QCLK period x 2
1
Input sample time = QCLK period x 16
Table 13-19. Multiplexed Channel Assignments and Pin Designations
Multiplexed Input Pins
Channel Number in CCW CHAN
Field
Port Pin
Name
Analog
Pin Name
Other Functions /
Descriptions
Pin Type
Binary
Decimal
ANw/A_PQB[0]
AN[00] to
AN[07]
—
Input
0000000 to
0000111
0to 7
ANx/A_PQB[1]
AN[08] to
AN[15]
—
Input
0001000 to
0001111
8to 15
ANy/A_PQB[2]
AN[16] to
AN[23]
—
Input
0010000 to
0010111
16 to 23
ANz/A_PQB[3]
AN[24] to
AN[31]
—
Input
0011000 to
0011111
24 to 31
—
RESERVED
—
0100000 to
0101001
32 to 41
—
RESERVED
—
0101010
42
—
RESERVED
—
0101011
43
Table 13-17. CCW Bit Descriptions (continued)
Bit(s)
Name
Description