ISLA112P50 Intersil, ISLA112P50 Datasheet - Page 18

• Manufacturer Part Number: ISLA112P50
• Description: 500MSPS A/D Converter
• Manufacturer: Intersil

since the internal DLL can take up to 52µs to regain lock
at 250MSPS.
By default after the device is powered on, the operational
state is controlled by the NAPSLP pin as shown in Table 3.
The power-down mode can also be controlled through
the SPI port, which overrides the NAPSLP pin setting.
Details on this are contained in “Serial Peripheral
Interface” on page 22. This is an indexed function when
controlled from the SPI, but a global function when
driven from the pin.
Data Format
Output data can be presented in three formats: two’s
complement, Gray code and offset binary. The data
format is selected via the OUTFMT pin as shown in
Table 4.
The data format can also be controlled through the SPI
port, which overrides the OUTFMT pin setting. Details on
this are contained in “Serial Peripheral Interface” on
page 22.
Offset binary coding maps the most negative input
voltage to code 0x000 (all zeros) and the most positive
input to 0xFFF (all ones). Two’s complement coding
simply complements the MSB of the offset binary
representation.
When calculating Gray code the MSB is unchanged. The
remaining bits are computed as the XOR of the current
bit position and the next most significant bit. Figure 35
shows this operation.
FIGURE 35. BINARY TO GRAY CODE CONVERSION
GRAY CODE
OUTFMT PIN
BINARY
NAPSLP PIN
AVDD
TABLE 4. OUTFMT PIN SETTINGS
AVDD
TABLE 3. NAPSLP PIN SETTINGS
AVSS
AVSS
Float
Float
11
11
10
10
18
9
9
Two’s Complement
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Offset Binary
Gray Code
Normal
MODE
MODE
Sleep
Nap
1
1
ISLA112P50
0
0
Converting back to offset binary from Gray code must be
done recursively, using the result of each bit for the next
lower bit as shown in Figure 36.
Mapping of the input voltage to the various data formats
is shown in Table 5.
VOLTAGE
Mid–Scale 100 00 000 00 00 000 00 000 00 00 110 00 000 00 00
Scale +
INPUT
Scale –
TABLE 5. INPUT VOLTAGE TO OUTPUT CODE MAPPING
Scale
Scale
FIGURE 36. GRAY CODE TO BINARY CONVERSION
1LSB
+Full
1LSB
+Full
–Full
–Full
GRAY CODE
BINARY
000 00 000 00 00 100 00 000 00 00 000 00 000 00 00
000 00 000 00 01 100 00 000 00 01 000 00 000 00 01
111 11 111 11 10 011 11 111 11 10 100 00 000 00 01
111 11 111 11 11 011 11 111 111 1 100 00 000 00 00
BINARY
OFFSET
11
11
10
10
COMPLEMENT
9
TWO’S
9
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www.DataSheet4U.com
March 30, 2010
GRAY CODE
1
1
FN7604.0
0
0