logic.
Figure 7 shows a timing diagram that might be used with a
typical digital signal processor such as a TI DSP. For the
Buffered Serial Port (BSP) on the TMS320C54X family,
CONV would tied to BFSX, CLK would be tied to BCLKX,
and DATA would be tied to BDR.
DATA FORMAT
The ADS7835 output data is in Binary Two’s Complement
format as shown in Table III. This table shows the ideal
output code for the given input voltage and does not include
SPI/QSPI INTERFACING
DESCRIPTION
ANALOG INPUT
DIGITAL OUTPUT
Figure 8 shows the timing diagram for a typical Serial
Peripheral Interface (SPI) or Queued Serial Peripheral Inter-
face (QSPI). Such interfaces are found on a number of
microcontrollers from various manufacturers. CONV would
be tied to a general purpose I/O pin (SPI) or to a PCX pin
(QSPI), CLK would be tied to the serial clock, and DATA
would be tied to the serial input data pin such as MISO
(Master In Slave Out).
Full-Scale Input
Range
Least Significant Bit
(LSB)(2)
BINARY TWO’S
COMPLEMENT
(1)
–VREF to +VREF
BINARY
CODE
HEX
CODE
(–VREF to +VREF)/4096
+Full Scale
Mid-Scale
Mid-Scale –1LSB
–Full Scale
2.49878V
0V
–0.00122V
–2.49878V
0111 1111 1111
0000 0000 0000
1111 1111 1111
1000 0000 0000
7FF
000
FFF
800
NOTES: (1) –2.5V to +2.5V when the internal reference is used. (2) 1.22mV
with a 2.5V reference.
Note the time tDRP shown in Figure 8. This represents the
maximum amount of time between CONV going LOW and
the start of the conversion clock. Since CONV going LOW
places the S/H in the hold mode and because the hold
capacitor loses charge over time, there is a requirement that
time tDRP be met as well as the maximum clock period
TABLE III. Ideal Input Voltages and Output Codes.
the effects of offset, gain, or noise.
DSP INTERFACING
CONV
15
16
1
2
3
12
13
14
15
16
1
2
3
4
CLK
D11
(MSB)
D0
(LSB)
D11
(MSB)
DATA
D10
D1
D10
D9
FIGURE 7. Typical DSP Interface Timing.
tDRP
tACQ
CONV
1
2
3
4
13
14
15
16
1
2
3
CLK
D11
(MSB)
D0
(LSB)
D11
(MSB)
DATA
D10
D1
FIGURE 8. Typical SPI/QSPI Interface Timing.
®
ADS7835
12
BB [ BURR-BROWN CORPORATION ]
