the DSP56002 must be programmed to enable the serial
interface when a LOW to HIGH transition on SCI occurs.
APPLICATIONS CIRCUIT
Figure 18 shows a multiplexed data acquisition circuit using
the ADS7812. The MPC508A provides the multiplexing
function while the OPA134 is configured as a Sallen-Key,
two-pole, unity gain lowpass filter.
The DSP56002 can also provide the CONV signal, as shown
in Figure 17. The receive and transmit sections of the
interface are decoupled (asynchronous mode) and the trans-
mit section is set to generate a word length frame sync every
other transmit frame (frame rate divider set to 2). The
prescale modulus should be set to produce a transmit frame
at twice the desired conversion rate.
DSP56002
ADS7812
SC2
CONV
BUSY
SC0
SRD
DATACLK
DATA
CS
SYN = 0 (Asychronous)
EXT/INT
GCK = 1 (Gated clock)
SCD2 = 1 (SC2 is an output)
SHFD = 0 (Shift MSB first)
WL1 = 0 WL0 = 1 (Word length = 12 bits)
FIGURE 17. DSP56002 Interface to the ADS7812. Processor Initiates Conversions.
+15V
C1
2.2nF
MPC508A
In 1
±10V
Full Scale
ADS7812
R1
1.4kΩ
R2
15.4kΩ
In 2
In 3
In 4
In 5
In 6
In 7
In 8
R1IN
BUSY
CONV
OPA134
R2IN
R3IN
BUF
C2
330pF
DATA
–15V
DATACLK
µP
A0
A1
A2
FIGURE 18. Multiplexed Data Acquisition Circuit.
®
17
ADS7812
BB [ BURR-BROWN CORPORATION ]
