National Instruments AT-MIO-64F-5, Руководство пользователя

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Register Map and Descriptions Chapter 4
AT-MIO-64F-5 User Manual 4-24 © National Instruments Corporation
ADC FIFO Register
Reading the ADC FIFO Register returns the oldest ADC conversion value stored in the ADC
FIFO. Whenever the ADC FIFO is read, the value read is removed from the ADC FIFO, thereby
leaving space for another ADC conversion value to be stored. Values are shifted into the ADC
FIFO whenever an ADC conversion is complete.
The ADC FIFO is emptied when all values it contains are read. Status Register 1 should be read
to determine the FIFO state before the ADC FIFO Register is read. If the ADC FIFO contains
one or more ADC conversion values, the ADCFIFOEF* bit is set in Status Register 1 and the
ADC FIFO Register can be read to retrieve a value. If the ADCFIFOEF* bit is cleared, the ADC
FIFO is empty, in which case reading the ADC FIFO Register returns meaningless information.
If the ADCFIFOHF* flag is clear in Status Register 1, the ADC FIFO is at least half-full with
conversion data, and 256 FIFO values can be read without checking the ADCFIFOEF* in Status
Register 1.
The values returned by reading the ADC FIFO Register are available in two different binary
formatsÐstraight binary, which generates only positive numbers, or twoÕs complement binary,
which generates both positive and negative numbers. The binary format used is determined by
the mode in which the ADC is configured. The bit pattern returned for either format is given as
follows:
Address: Base a 00 (hex)
Type: Read-only
Word Size: 16-bit
Bit Map:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
MSB LSB
Bit Name Description
15-0 D<15..0> Local data bus bits. When the ADC FIFO is addressed, these bits
are the result of a sign-extended 12-bit ADC conversion. Values
read range from 0 to 4,095 decimal (0x0000 to 0xFFF) when the
ADC is in unipolar mode, and -2,048 to +2,047 decimal (0xF800
to 0x7FF) when the ADC is in bipolar mode.
The A/D conversion result can be returned from the ADC FIFO as a twoÕs complement or
straight binary value depending on the input mode set by the ADC_BIP bit in the configuration
memory location for the converted channel. If the analog input circuitry is configured for the
unipolar input range, straight binary format is implemented. Straight binary format returns
numbers between 0 and 4,095 (decimal) when the ADC FIFO Register is read. If the analog
input circuitry is configured for the bipolar input ranges, twoÕs complement format is used.
TwoÕs complement format returns numbers between -2,048 and +2,047 (decimal) when the ADC
FIFO Register is read. Table 4-7 shows input voltage versus A/D conversion value for straight
binary format and unipolar input range. Table 4-8 shows input voltage versus A/D conversion
value for twoÕs complement format and bipolar input range.