mc68hc05jp6pe Freescale Semiconductor, Inc, mc68hc05jp6pe Datasheet - Page 130

• Manufacturer Part Number: mc68hc05jp6pe
• Description: M68hc05 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Analog Subsystem
8.7.1.2 External Absolute Reference
General Release Specification
130
Change in reference
Change in magnitude of
Non-linearity of ramp
Change in magnitude of
Frequency shift in
Frequency shift in
Sampling capacitor
Internal voltage divider
Input offset voltage of
Noise internal to MCU
Noise external to MCU
voltage
ramp current source
current source vs.
voltage
ramp capacitor
internal low-power
oscillator
external oscillator
leakage
ratio
comparator 2
Error Source
Provide closer tolerance reference
Not adjustable
Not adjustable
Provide closer tolerance ramp capacitor
Use external oscillator with crystal
Provide closer tolerance crystal
Use faster conversion times
Not adjustable
Not adjustable
Close decoupling at V
Close decoupling of power supply, low
If a stable external source is provided, the reference measurement point
can be any one of the channel selected pins from PB1 through PB4. In
this case, the reference reading can be taken by setting the MUX bit in
the AMUX which connects channel selection bus to the pin connected to
the external reference source. If the external reference is greater than
V
divided input.
Table 8-6. Absolute Voltage Reading Errors
and reduce supply source impedance
source impedances, good board
layout, use of multi-layer board
DD
–1.5 volts, then the DHOLD bit should be used to select the 1/2
In Hardware
Analog Subsystem
DD
Accuracy Improvements Possible
and V
SS
pins
Calibration and storage of reference source
Compare unknown with recent
Calibration and storage of voltages at 1/4,
Compare unknown with recent
Compare unknown with recent
Compare unknown with recent
Compare unknown with recent
Compare unknown with recent
Sum two readings on reference or
Average multiple readings on both the
Average multiple readings on both the
MC68HC05JJ6/MC68HC05JP6
over temperature and supply voltage
measurement from reference
1/2, 3/4, and FS
measurement from reference
measurement from reference
measurement from reference
measurement from reference
measurement from reference OR avoid
use of divided input
unknown using INV and INV control bit
and divide by 2 (average of both)
reference and the unknown voltage
reference and the unknown voltage
In Software
Freescale Semiconductor
—
Rev. 3.2