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R01UH0336EJ0102 Rev.1.02
Page 1301 of 1538
Jul 17, 2014
V850E2/PG4-L
Section 23 A/D Converter
4. Disable the hardware trigger for all channel groups by setting the
ADCA0TSEL0, ADCA0TSEL1, and ADCA0TSEL2 registers, or the
ADCA0T2ETS1 and ADCA0T2ETS0, ADCA0T1ETS1 and
ADCA0T1ETS0, and ADCA0T0ETS1 and ADCA0T0ETS0 bits in the
ADCA0CTL1 register. Also, control other channel groups so that
conversion does not proceed during diagnosis to detect when the pin for
the target channel is open circuit.
5. Set the registers to enable continuous A/D conversion on the target
channel, and start conversion with either of the following methods.
– When channel group 0 is to be used, specify continuous scan mode by
setting ADCA0MD1 and ADCA0MD0 in ADCA0CTL1 to 01h before
starting A/D conversion.
– When channel group 1 or 2 is to be used, set TAUB to input a trigger
signal at a fixed interval (the time for one A/D conversion), and set
ADCA0TSEL1 or ADCA0TSEL2 to accept only the signal from TAUB as
the trigger to start A/D conversion.
6. As continuous A/D conversion proceeds, transfer each result of conversion
to another area (on-chip RAM) by interrupt processing or DMA. These data
are used in determining the result of the diagnosis.
7. On completion of A/D conversion the specified number of times*, check the
results of A/D conversion for values that decline to almost 0 V and are less
than 0.2 V. If such values are found, the analog input pin for the target
channel is judged to have been disconnected.
8. When multiple channels are to be targets for diagnosis, change the
settings for the target channel in steps 2 and 3, then repeat steps 5 to 7.
Note 1.
When AVDD = 5 V, calculate the number of times continuous conversion must
proceed to detect an open-circuit pin (corresponding to the time taken for 5 V
to change to 0.2 V due to the 15-pF pin capacitance) from the AD conversion
time at the number of conversions required to make the total conversion time
equal to at least 58
μ
s.
The reference voltage (0.2 V) and total conversion time (58
μ
s) are reference
values. Those values must be fixed after exhaustive evaluation on the user
system condition.
Caution
The diagnostic function for the detection of open pins is designed for detecting
the disconnection of analog input pins from the board and the disconnection of
bonding wires; Due to the external capacitance, it cannot detect the
disconnection of wiring on the sensor side.
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