CDB5378 datasheet(22/72 Pages) CIRRUS

22 / 72 page

CDB5378

DS639DB3

2.3.1.2

Configuration - SPI Port

On CDB5378, configuration of the digital filter is through the SPI port by the on-board 8051 microcontrol-

ler, which receives commands from the PC evaluation software via the USB interface. Evaluation software

commands can write/read digital filter registers, specify digital filter coefficients and start/stop digital filter

operation. Alternately, the digital filter can automatically load configuration information from an on-board

serial EEPROM.

The configuration method for the digital filter is selected by the BOOT signal from a dip switch (S1, #4).

By default the BOOT signal is set low (S1, #4 - LO) to indicate configuration information is written by the

microcontroller. If BOOT is instead set high (S1, #4 - HI), the digital filter attempts to automatically read

configuration information from the serial EEPROM after reset. Configuration information is initially written

into the serial EEPROM by jumpering its chip select input (EECS) to the microcontroller chip select output

(SS) and sending EEPROM programming commands and data from the PC evaluation software.

2.3.1.3

Phase Locked Loop

To make synchronous analog measurements throughout a distributed system, a synchronous system

clock is required to be provided to each measurement node. For evaluation testing purposes, a BNC clock

input on CDB5378 can receive an external system clock and create a synchronous local clock using the

CS5378 PLL.

The system clock into the BNC clock input is applied to the CS5378 CLK input by selecting CLK_EXT on

the DIGITAL FILTER CLOCK jumper (J16). The CS5378 PLL input frequency is specified at reset by the

state of the GPIO[4..6]:PLL[0..2] pins, as detailed in the CS5378 data sheet.

Specification

Value

Input Clock Frequency

1.024, 2.048, 4.096 MHz

Distributed Clock Synchronization

± 240 ns

Maximum Input Clock Jitter, RMS

1 ns

Specification

Value

PLL Internal Clock Frequency

32.768 MHz

Maximum Jitter, RMS

300 ps

Loop Filter Architecture

Internal

CDB5378 Datasheet(PDF) 22 Page - Cirrus Logic