Texas Instruments ADS1278-SP, User Manual, Page: 19 / 32

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ADS1278EVM-CVAL Hardware Details
19 SBAU324 – September 2018
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ADS1278EVM-CVAL Evaluation Module User's Guide
• FS format configures the signals as follows:
– The SCLK input of the converter is driven by the serial port signal CLKR, pin J4.5 .
– The signal from the selected clock source is connected to the CLKX pin ( J4.3 ), allowing the serial
port of a processor to be synchronized to the converter's master clock.
– The CLK input of the converter is driven by the CLKR signal ( J4.5 ). This ensures that the CLK and
SCLK signals have the same phase and the correct ratio as outlined in the data sheet of the
device.
– Port P10 of the I
2
C port expander U8 is connected to a logic low level, so that the position of S6
can be read back by software.
For use with the MMB0 motherboard, the jumpers on S6 must be installed in the FS positions, which is the
factory default setting. See Figure 2 .
Switching to SPI format will allow users to connect the EVM to any SPI-compatible processor not
supporting the frame-sync mode. If this format is selected, keep in mind that the high-speed mode will not
operate at full speed (32.768 MHz) because of the limitations outlined in the device product data sheet.
5.5.2 Serial Data Interface, J4
This header/socket provides access to the digital control and serial data pins of the ADC.
All logic levels on J4 are 3.3-V CMOS, except for the I
2
C pins. These pins conform to 3.3-V I
2
C rules.
Table 9 describes the J4 serial interface pins.
(1)
Pin 1 is top left-hand corner, located next to reference designator.
(2)
DOUT1 buffered through a D flip-flop. See Section 5.5.3.1 below.
Table 9. J4: Serial Interface Header
Function Signal Name Designator Signal Name Function
Synchronize channels input SYNC 1
(1)
2 MODE0 Select bit 0 of converter MODE
SPI clock SCLK 3 4 DGND Digital ground
SCLK clock CLKR 5 6 MODE1 Select bit 1 of converter MODE
DRDY/FSYNC source 1 DRDY/FSYNC 7 8 FORMAT0
Select bit 0 of FORMAT to select
Frame-Sync/SPI Protocol
DRDY/FSYNC source 2 DRDY/FSYNC 9 10 DGND Digital ground
ADS1278 SPI data in DIN 11 12 FORMAT1
Select bit 1 of FORMAT to select
Frame-Sync/SPI Protocol
ADS1278 data out DOUT1
(2)
13 14 FORMAT2
Select bit 2 of FORMAT to select
Frame-Sync/SPI Protocol
DRDY/FSYNC to DSP (interrupt) DRDY/FSYNC 15 16 SCL I
2
C clock
Can be used to provide a clock
from a processor
CLK 17 18 DGND Digital ground
Clock source select (SW mode) CLK Select 19 20 SDA I
2
C data
Some pins on J5 have weak pull-up/down resistors. These resistors provide default settings for many of
the control pins. Many pins on J5 correspond directly to ADS1278-SP pins. See the ADS1278-SP product
data sheet for complete details on these pins.
5.5.3 Data Output Signals
5.5.3.1 DOUT on Digital Interface J4
In TDM mode, the data from all eight channels can be observed on the DOUT1 pin of the converter. The
DOUT1 signal is used by the MMB0 motherboard to read back and display all the channels. The digital
data output pin on the digital interface header
J4 is connected to DOUT1 signal via a D flip-flop. The D
flip-flop provides a half cycle delay in order to align the data correctly to reach the higher speeds of the
device. Otherwise, the propagation delay from the MSB in Frame Sync mode may result in missing the
MSB out of the data word.