CR16MES5 Datasheet, PDF (72/99 Pages) National Semiconductor (TI) – Family of CompactRISC 16-Bit Microcontrollers

18.1.2 Single Channel, Continuous Conversion Mode
In the single channel, continuous conversion mode, the A/D
Converter performs conversions repeatedly using the same
specified channel.
The software starts a conversion sequence by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using the same channel, pausing only for
the programmable sampling delay time used in all conver-
sion operations. It loads the four results into the A/D data reg-
isters in sequence, starting with ADDATA0 and ending with
ADDATA3. After it loads all four registers, it sets the EOC
(end of conversion) bit. If the A/D Converter interrupt is en-
abled, an interrupt to the CPU is generated at this time.
The START bit remains set until cleared by the software. If
the software does not clear the START bit, the A/D Converter
continues performing conversions using the same input
channel, storing the results in ADDATA0 following ADDATA3.
To prevent an overrun error, the software must read the re-
sults from the data registers before the A/D Converter writes
the next result into ADDATA0 following ADDATA3.
When the software clears the START bit, the A/D Converter
first completes the conversion currently in progress, then
stops and sets the EOC bit. A 2-bit buffer pointer in the
ADCST register points to the register containing the final re-
sult.
18.1.3 4-Channel Scan, Single Conversion Mode
In the 4-channel scan, single conversion mode, the A/D Con-
verter performs four conversions using four adjacent input
channels.
The software starts the conversion sequence by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using four adjacent channels, starting with
the specified channel and pausing only for the programmable
sampling delay time. It loads the four results into the A/D data
registers in sequence, starting with ADDATA0 and ending
with ADDATA3. After it loads all four registers, it clears the
START bit and sets the EOC (end of conversion) bit. If the A/
D Converter interrupt is enabled, an interrupt to the CPU is
generated at this time.
18.1.4 Channel Scan, Continuous Conversion Mode
In the 4-channel scan, continuous conversion mode, the A/D
Converter performs conversions repeatedly using four adja-
cent input channels.
The software starts conversion operations by setting the
START bit. The A/D Converter performs four A/D conver-
sions in sequence using four adjacent channels, starting with
the specified channel and pausing only for the programmable
sampling delay time. It loads the four results into the A/D data
registers in sequence, starting with ADDATA0 and ending
with ADDATA3. After it loads all four registers, it sets the EOC
(end of conversion) bit. If the A/D Converter interrupt is en-
abled, an interrupt to the CPU is generated at this time.
The START bit remains set until cleared by the software. If
the software does not clear the START bit, the A/D Converter
continues performing conversions, repeating the same se-
quence using the same four input channels and the same se-
quence of data registers. To prevent an overrun error, the
software must read the results from the data registers before
the A/D Converter writes the next result into ADDATA0.
When the software clears the START bit, the A/D Converter
first completes the 4-channel conversion sequence currently
in progress, then stops and sets the EOC bit.
18.2 A/D CONVERTER REGISTERS
The software controls the A/D Converter and reads the A/D
results by accessing the ADC registers. There are eight such
registers:
• ADC Status Register (ADCST)
• ADC Control 1 Register (ADCCNT1)
• ADC Control 2 Register (ADCCNT2)
• ADC Control 3 Register (ADCCNT3)
• ADC Data Registers (ADDATA0 through ADDATA3)
18.2.1 ADC Status Register (ADCST)
The ADCST register is a byte-wide register that indicates the
current status of the A/D Converter. One bit in this register,
the OVF flag bit, is cleared by writing a 1 to its bit position.
The other bits are read-only bits, so the values written to
them are ignored. Upon reset, the register is set to 30 hex.
The register format is shown below.
7 65 4
3
2
1
0
Reserved BUFPTR Reserved OVF BUSY EOC
EOC
BUSY
OVF
BUFPTR
End of Conversion. This read-only bit reports
the status of the most recent A/D Converter op-
eration. When cleared to 0, it indicates that the
conversion is not complete. When set to 1, it in-
dicates that the conversion is complete. The
hardware sets this bit when it places the con-
version results in the buffer and clears it when
any of the data registers are read.
ADC Busy. This read-only bit is set to 1 when
the A/D Converter is busy converting data and
is cleared to 0 when the A/D Converter is idle
or disabled.
Overflow. The hardware sets this bit to 1 when
the A/D Converter finishes a conversion and at-
tempts to store the results in one of the data
registers (ADDATA0-ADDATA3) while the reg-
ister is full. When this happens, the A/D Con-
verter overwrites the data in the data register,
sets the OVF flag, and continues operating.
The OVF flag remains set until cleared by the
software. The software clears the flag by writ-
ing a 1 to it. Writing a 0 to this bit has no effect.
Buffer Pointer. This 2-bit, read-only field identi-
fies the data register that was most recently
written with new data:
00 = ADDATA0
01 = ADDATA1
10 = ADDATA2
11 = ADDATA3
This register is initialized to 11 when a new con-
version is started (when ADCCNT2.START is
changed from 0 to 1) and is automatically incre-
mented every time a result is written to buffers
ADDATA0-ADDATA3. The result is a four-entry
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