Texas Instruments ADS794xEVM, Руководство пользователя, Страница: 7 / 31

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Digital Interface
7 SBAU194B – August 2011 – Revised September 2017
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Copyright © 2011–2017, Texas Instruments Incorporated
ADS794xEVM and ADS794xEVM-PDK
3 Digital Interface
Samtec part numbers SSW-110-22-F-D-VS-K and TSM-110-01-L-DV-P provide a convenient 10-pin, dual-
row, header/socket combination at P1. This header/socket provides access to the digital control pins of the
ADC. Consult Samtec at
http://www.samtec.com or call 1-800-SAMTEC-9 for a variety of mating
connector options.
Table 4 summarizes the pinouts for digital interface P1.
Table 4. P1: Serial Interface Header
Pin Number Signal Description
P1.1 CS Chip select input. Pulled high with 10-k Ω resistor.
P1.3 SCLK Serial clock input
P1.7 CS
Chip select input. This pin is intended to be used by
the MMB0 motherboard
P1.11 SDI or MOSI SDI or MOSI input
P1.13 SDO or MISO SDO or MISO output
P1.19 PDEN
Power-down input (active high). Pulled down with
10-k
Ω resistor.
P1.4, P1.10, and P1.18 GND Digital ground connections
P1.16, P1.20 I
2
C bus
I
2
C bus; used only used to program the U4
EEPROM on the EVM board
P1.2, P1.5-6, P1.8-9,
P1.12, P1.14-15, and
P1.17
Unused Unused
3.1 Serial Interface (SPI)
The ADS794x ADC uses SPI serial communication in mode 0 (CPOL = 0, CPHA = 0). Because the serial
clock (SCLK) frequency can be as fast as 40 MHz, the ADS794xEVM offers 47-
Ω resistors between the
SPI signals and P1 to aid with signal integrity. Typically, in high-speed SPI communication, fast signal
edges can cause overshoot; these 47-
Ω resistors slow down the signal edges in order to minimize signal
overshoot.
3.2 ADS794x Channel Select as SDI (MISO)
The ADS794x ADC offers direct control over the internal multiplexer using pin 11. The ADS794xEVM uses
a flip-flop (see U9 in the attached schematic) to convert this pin into a typical SPI SDI (MOSI) pin. This
architecture takes advantage of the SPI full-duplex data transmission sequence to control channel
selection at the same time conversion data are acquired. The digital word
0x000 can be used to select
channel 0, and the word 0xFFFF can be used to select channel 1.
3.3 I
2
C Bus for Onboard EEPROM
The ADS794xEVM has an I
2
C bus to communicate with the onboard EEPROM that records the board
name and assembly date. It is not used in any form by the ADS794x converter.