MC68HC705JP7CDW Freescale Semiconductor, MC68HC705JP7CDW Datasheet - Page 89

• Manufacturer Part Number: MC68HC705JP7CDW
• Description: IC MCU 8BIT 28-SOIC
• Manufacturer: Freescale Semiconductor
• Series: HC05r

Specifications of MC68HC705JP7CDW

• Core Processor: HC05
• Core Size: 8-Bit
• Speed: 2.1MHz
• Connectivity: SIO
• Peripherals: POR, Temp Sensor, WDT
• Number Of I /o: 22
• Program Memory Size: 6KB (6K x 8)
• Program Memory Type: OTP
• Ram Size: 224 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 4x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

8.6 Voltage Measurement Methods
The methods for obtaining a voltage measurement can use software techniques to express these
voltages as absolute or ratiometric readings.
In most applications the external capacitor, the clock source, the reference voltage, and the charging
current may vary between devices and with changes in supply voltage or ambient temperature. All of
these variations must be considered when determining the desired resolution of the measurement. The
maximum and minimum extremes for the full scale count will be:
The minimum count should be the desired resolution, and the counting mechanism must be capable of
counting to the maximum. The final scaling of the count will be by a math routine which calculates:
Where:
When V
voltage will be determined as an absolute reading. If V
the unknown voltage will be determined as a ratio of V
If the unknown voltage applied to the comparator is greater than its common-mode range (V
then the external capacitor will try to charge to the same level. This will cause both comparator inputs to
be above the common-mode range and the output of the comparator will be indeterminate. In this case
the comparator output flags may also be set even if the actual voltage on the positive input (+) is less than
the voltage on the negative input (–). All A/D conversion methods should have a maximum time check to
determine if this case is occurring.
Once the maximum timeout detection has been made, the state of the comparator outputs can be tested
to determine the situation. However, such tests should be carefully designed when using modes 1, 2, or
3 as these modes cause the immediate automatic discharge of the external ramping capacitor before any
software check can be made of the output state of comparator 2.
Freescale Semiconductor
V
V
N
N
N
REF
X
X
REF
OFF
REF
= Known reference voltage
= Unknown voltage between V
= Conversion count for unknown voltage
= Conversion count for known reference voltage (V
= Conversion count for minimum reference voltage (V
is a stable voltage source such as a zener or other reference source, then the unknown
All A/D conversion methods should include a test for a maximum elapsed
time to detect error cases where the inputs may be outside of the design
specification.
MC68HC705JJ7 • MC68HC705JP7 Advance Information Data Sheet, Rev. 4.1
N
N
FSMAX
FSMIN
V
= C
X
= C
= V
EXTMAX
EXTMIN
REF
SS
x (N
x V
x V
and V
X
FSMIN
FSMAX
– N
NOTE
REF
OFF
x f
REF
DD
x f
) / (N
OSCMIN
, or a ratiometric reading.
OSCMAX
is the supply source to the device (V
REF
REF
SS
)
/ (P x I
– N
)
/ (P x I
OFF
CHGMAX
CHGMIN
)
Voltage Measurement Methods
)
)
DD
–1.5 volts),
DD
), then
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