QADC64E Enhanced Mode Operation
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
14-37
Therefore, conversion time requires a minimum of 14 QCLK clocks (seven µs with a 2.0-MHz QCLK). If
the maximum final sample time period of 8 QCLKs is selected, the total conversion time is 20 QCLKs (10
µs with a 2.0-MHz QCLK)
illustrates the timing for conversions.
Figure 14-21. Conversion Timing
14.3.12 Channel Decode and Multiplexer
The internal multiplexer selects one of the 16 analog input signals for conversion. The selected input is
connected to the sample buffer amplifier. The multiplexer also includes positive and negative stress
protection circuitry, which prevents deselected channels from affecting the selected channel when current
is injected into the deselected channels. Refer to
Appendix F, “Electrical Characteristics
,” for specific
current levels.
14.3.13 Sample Buffer Amplifier
The sample buffer is used to raise the effective input impedance of the A/D converter, so that external
components (higher bandwidth or higher impedance) are less critical to accuracy. The input voltage is
buffered onto the sample capacitor to reduce crosstalk between channels.
14.3.14 Digital to Analog Converter (DAC) Array
The digital to analog converter (DAC) array consists of binary-weighted capacitors and a resistor-divider
chain. The reference voltages, V
RH
and V
RL
, are used by the DAC to perform ratiometric conversions. The
DAC also converts the following three internal channels:
•
V
RH
— Reference voltage high
•
V
RL
— Reference voltage low
•
(V
RH
– V
RL
)/2 — Reference voltage
The DAC array serves to provide a mechanism for the successive approximation A/D conversion.
Sample
Time
“Final” Sample
Time
Resolution (“Conv”)
Time
Sample Time
Successive Approximation Resolution
Sequence
2 cycles
N
cycles:
10 cycles
QCLK
(2 or 8)
“Buffer”
Summary of Contents for MPC561
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Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...