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Digital Interface
3
Digital Interface
Connector J19 (Samtec part number ERF8-025-01-L-D-RZ-L-TR socket strip connector) provides the
digital I/O connections between the ADS8688EVM board and the Simple Capture card. Consult Samtec at
or call 1-800-SAMTEC-9 for a variety of mating connector options.
summarizes
the pin outs for connector J19.
Table 8. Connector J19 Pin Out
Pin Number
Signal
Description
J19.1
DAISY
Daisy input for the ADC
J19.4
EVM_PRESENT
EVM present, active low (connected to GND)
J19.5
REFSEL
Reference selection input for the ADC
J19.6
RST/PD
Reset or power-down input for the ADC
J19.8
A
No connection
J19.11
EVM_ID_SDA
I
2
C data for the onboard EEPROM
J19.12
EVM_ID_SCL
I
2
C clock for the onboard EEPROM
J19.13
3V3_SDCC
3.3-V digital supply from the Simple Capture card
J19.14
5V_SDCC
Unregulated 5-V supply from the Simple Capture card
J19.33, J19.34
SCLK
Clock input for the ADC
J19.35
CS
Chip-select input for the ADC
J19.38
SDI
Data input for the ADC
J19.39
SDO
Data output from the ADC
J19.45-49
EVMSDxxxxx
Digital connections for the onboard SD card
J19.2, J19.10, J19.16, J19.50
GND
Ground connections
3.1
Serial Interface (SPI)
The ADS8688 device uses SPI serial communication in mode 1 (CPOL = 0, CPHA = 1) with clock speeds
up to 17 MHz. The ADS8868xEVM offers 49.9-
Ω
resistors between the SPI signals and J19 to aid with
signal integrity. Typically, in high-speed SPI communication, fast signal edges can cause overshoot; these
49.9-
Ω
resistors slow down the signal edges in order to minimize signal overshoot.
3.2
I
2
C Bus for the Onboard EEPROM
The ADS8688EVM has an I
2
C bus that records the board name and assembly date to communicate with
the onboard EEPROM. The bus is not used in any form by the ADS8688 converter.
3.3
SD Card
The ADS8688EVM has an SD card that contains the software files for the Simple Capture card. The
contents of the SD card must not be deleted or altered.
8
ADS8688EVM-PDK Evaluation Module
SBAU230A – August 2014 – Revised December 2014
Copyright © 2014, Texas Instruments Incorporated