QADC64E Legacy Mode Operation
MPC561/MPC563 Reference Manual, Rev. 1.2
13-36
Freescale Semiconductor
Figure 13-22. Bypass Mode Conversion Timing
13.4.2
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.
13.4.3
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.
13.4.4
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.
Resolution begins with the most significant bit (MSB) and works down to the least significant bit (LSB).
The switching sequence is controlled by the comparator and successive-approximation register (SAR)
logic.
•
Sample capacitor —
The sample capacitor is employed to sample and hold the voltage to be
converted.
Sample
Time
Resolution
Time
Sample
Time
Successive Approximation Resolution
Sequence
N cycles:
10 cycles
QCLK
(2, 4, 8, 16)
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
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...