ADUC812(1999) 데이터 시트보기 (PDF) - Analog Devices
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ADUC812 Datasheet PDF : 31 Pages
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ADuC812
many applications this autocalibration download function suf-
fices. Alternatively, a device calibration can be easily initiated by
user software to compensate for significant changes in operating
conditions (CLK frequency, analog input range, reference volt-
age and supply voltages).
This in-circuit software calibration feature allows the user to
remove various system and reference related errors (whether it
be internal or external reference) and to make use of the full
dynamic range of the ADC by adjusting the analog input range
of the part for a specific system. Contact Analog Devices, Inc.
for further details on the implementation of the software calibra-
tion routine in your applications.
ADC MODES OF OPERATION
Typical Operation
Once configured via the ADCCON 1-3 SFRs (shown previ-
ously) the ADC will convert the analog input and provide an
ADC 12-bit result word in the ADCDATAH/L SFRs. The top
four bits of the ADCDATAH SFR will be written with the
channel selection bits to identify the channel result. The format
of the ADC 12-bit result word is shown in Figure 5.
ADCDATAH SFR
CH–ID
TOP 4 BITS
HIGH 4 BITS OF
ADC RESULT WORD
ADCDATAL SFR
LOW 8 BITS OF THE
ADC RESULT WORD
Figure 5. ADC Result Format
ADC DMA Mode
The on-chip ADC has been designed to run at a maximum speed
of one sample every 5 µs (i.e., 200 kHz sampling rate). Therefore,
in an interrupt driven routine the user software is required to ser-
vice the interrupt, read the ADC result and store the result for
further post processing, all within 5 µs otherwise the next ADC
sample could be lost. In applications where the ADuC812 can-
not sustain the interrupt rate, an ADC DMA Mode is provided.
The ADC DMA Mode is enabled via the DMA enable bit
(ADCCON2.6), which allows the ADC to sample continuously
as per configuration in ADCCON SFRs. Each sample result is
written into an external Static RAM (mapped in the data memory
space) without any interaction from the ADuC812 core. This
mode ensures the ADuC812 can capture a contiguous sample
stream even at full speed ADC update rates.
Before enabling ADC DMA mode the user must first configure
the external SRAM to which the ADC samples will be written.
This consists of writing the required ADC DMA channels into
the channel ID bits (the top four bits) in the external SRAM. A
typical preconfiguration of external memory is shown in Figure 6.
Once the external data memory has been preconfigured, the
DMA address pointer (DMAP, DMAH and DMAL) SFRs are
written. These SFRs should be written with the DMA start
address in external memory. In Figure 6, for example, the DMA
start address is 000000H. The 3-byte start address should be
written in the following order: DMAL, DMAH and DMAP.
The end of a DMA table is signified by writing “1111” into the
channel selection bits field.
00000AH 1 1 1 1
00 11
00 11
STOP COMMAND
REPEAT LAST CHANNEL
FOR A VALID STOP
CONDITION
CONVERT ADC CH#3
100 0
CONVERT TEMP SENSOR
010 1
CONVERT ADC CH#5
000000H 0 0 1 0
CONVERT ADC CH#2
Figure 6. Typical DMA External Memory Preconfiguration
The DMA Enable bit (ADCCON2.6, DMA) can now be set to
initiate the DMA conversion and transfer of the results sequen-
tially into external memory. Remember that the DMA mode
will only progress if the user has preconfigured the ADC
conversion time and trigger modes via the ADCCON1 and 2
SFRs. The end of DMA conversion is signified by the ADC
interrupt bit ADCCON2.7.
At the end of ADC DMA Mode, the external data memory
contains the new ADC conversion results as shown in Figure 7.
It should be noted that the channel selection bits are still present
in the result words to identify the individual conversion results.
00000AH 1 1 1 1
00 11
00 11
100 0
010 1
000000H 0 0 1 0
STOP COMMAND
NO CONVERSION
RESULT WRITTEN HERE
CONVERSION RESULT
FOR ADC CH#3
CONVERSION RESULT
FOR TEMP SENSOR
CONVERSION RESULT
FOR ADC CH#5
CONVERSION RESULT
FOR ADC CH#2
Figure 7. Typical External Memory Configuration Post
ADC DMA Operation
Micro Operation during ADC DMA Mode
During ADC DMA mode the MicroConverter core is free to
continue code execution, including general housekeeping and
communication tasks. However, it should be noted that MCU
core accesses to Ports 0 and 2 (which, of course, are being used
by the DMA controller) are gated “OFF” during ADC DMA
mode of operation. This means that even though the instruction
that accesses the external Ports 0 or 2 will appear to execute, no
data will be seen at these external port pins as a result.
The MicroConverter core is interrupted once the requested
block of DMA data has been captured and written to external
memory allowing the service routine for this interrupt to post-
process the data without any real time, timing constraints.
SFR Interface to the DAC Block
The ADuC812 incorporates two 12-bit DACs on-chip. DAC
operation is controlled via a single control special function
register and four data special function registers, namely:
DAC0L/DAC1L – Contains the lower 8-bit DAC byte.
DAC0H/DAC1H – Contains the high 4-bit DAC byte.
DACCON
– Contains general purpose control bits
required for DAC0 and DAC1 operation.
REV. 0
–11–
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