PCIe-24DSI32
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General Standards Corporation Ph:(256)880-8787 FAX:(256)880-8788 Email: [email protected]
3-6
3.5.2.2 Input Data Format
Input data values can be represented either in offset binary format by asserting the OFFSET
BINARY control bit HIGH (default state) in the BCR, or in two's complement format by clearing
the control bit LOW. Both coding conventions are illustrated for 16-Bit data in Table 3.5.2.2.
Table 3.5.2.2. Analog Input Data Coding; 16-Bit Data Field
DIGITAL
VALUE (Hex)
ANALOG INPUT LEVEL
OFFSET BINARY
TWO'S COMPLEMENT
Positive Full Scale minus 1 LSB
FFFFh
7FFFh
Zero plus 1 LSB
8001h
0001h
Zero
8000h
0000h
Zero minus 1 LSB
7FFFh
FFFFh
Negative Full Scale plus 1 LSB
0001h
8001h
Negative Full Scale
0000h
8000h
Positive Full Scale
is a positive level that equals the selected input voltage range for the board
(e.g.: +5.000 Volts for the ±5V range).
Negative Full Scale
is the negative equivalent of
positive full-scale.
Full-scale Range
(FSR
)
is the total input voltage range. For 16-Bit data,
one LSB equals the full-scale range divided by 65,536. (e.g.: 152.59 microvolts for the ±5V
range).
3.5.3 Buffer Control Register
The buffer control register (Table 3.5.3) contains the threshold value for the buffer status flag,
and also provides control bits for clearing the buffer and for disabling the buffer input.
Table 3.5.3. Buffer Control Register
Offset: 0000 0020h
Default: 0X03 FFFEh *
BIT FIELD
MODE
DESIGNATION
FUNCTION
D[17..00]
R/W
BUFFER THRESHOLD
Buffer Flag Threshold (duplicated in the BCR)
D[18]
R/W
DISABLE BUFFER INPUT
Disables ADC inputs to the buffer
D[19]
R/W
CLEAR BUFFER **
Clears (empties) the buffer
D[21..20]
R/W
DATA WIDTH
Controls the width of the buffer data field as:
0 => 16 bits
1 => 18 bits
2 => 20 bits
3 => 24 bits.
D[23..22]
RO
(Reserved)
---
D[24]
R/W
BUFFER OVERFLOW ***
Reports buffer overflow (Write on full)
D[25]
R/W
BUFFER UNDERFLOW ***
Reports buffer underflow (Read on empty)
D[31..26]
RO
(Reserved)
---
* Changes to 0103 FFFEh when the buffer fills.
** Clears automatically. *** Clear by writing LOW, or by board reset.