ANALOG-TO-DIGITAL CONVERTER
M68HC16 Z SERIES
8-12
USER’S MANUAL
8.7.6 Conversion Timing
Total conversion time is made up of initial sample time, transfer time, final sample time,
and resolution time. Initial sample time is the time during which a selected input chan-
nel is connected to the sample buffer amplifier through a sample capacitor. During
transfer time, the sample capacitor is disconnected from the multiplexer, and the RC
DAC array is driven by the sample buffer amp. During final sampling time, the sample
capacitor and amplifier are bypassed, and the multiplexer input charges the RC DAC
array directly. During resolution time, the voltage in the RC DAC array is converted to
a digital value, and the value is stored in the SAR.
Initial sample time and transfer time are fixed at two ADC clock cycles each. Final sam-
ple time can be 2, 4, 8, or 16 ADC clock cycles, depending on the value of the STS
field in ADCTL0. Resolution time is ten cycles for 8-bit conversion and twelve cycles
for 10-bit conversion.
Transfer and resolution require a minimum of 16 ADC clocks (8
µ
s with a 2.1 MHz ADC
clock) for 8-bit resolution or 18 ADC clocks (9
µ
s with a 2.1 MHz ADC clock) for 10-bit
resolution. If maximum final sample time (16 ADC clocks) is used, total conversion
time is 15
µ
s for an 8-bit conversion or 16
µ
s for a 10-bit conversion (with a 2.1 MHz
ADC clock).
Figures 8-2
and
illustrate the timing for 8- and 10-bit conversions, respectively.
These diagrams assume a final sampling period of two ADC clocks.
Figure 8-2 8-Bit Conversion Timing
1
CYCLE
2
CYCLES
1
CYCLE
1
CYCLE
1
CYCLE
1
CYCLE
1
CYCLE
1
CYCLE
SAR0
SAR7
SAR6
SAR5
SAR4
SAR3
SAR2
SAR1
CH 8
CH 7
CH 6
CH 5
CH 4
CH 3
CH 2
CH 1
SCF FLAG SET HERE AND SEQUENCE
ENDS IF IN THE 4-CHANNEL MODE
SCF FLAG SET HERE AND SEQUENCE
ENDS IF IN THE 8-CHANNEL MODE
SAMPLE AND TRANSFER
PERIOD
1
CYCLE
SUCCESSIVE APPROXIMATION
SEQUENCE
END
16
1
6 CYCLES
TRANSFER CONVERSION TO
RESULT REGISTER AND SET
CCF
RESOLUTION TIME
INITIAL
SAMPLE
TIME
TRANSFER
TIME
FINAL
SAMPLE
TIME
EOC
16 ADC 8-BIT TIM 1
(2 ADC CLOCKS)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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