National Instruments PCI-6703 User Manual - Bus Interface Circuitry

Chapter 4

Hardware Overview

PCI/PXI-6703/6704 User Manual

4-2

www.natinst.com

Bus Interface Circuitry

The bus interface circuitry monitors the PCI or PXI bus. If the bus address 

matches the 6703/6704 device’s address, the board is enabled and the 

corresponding register on the 6703/6704 is accessed.

I/O Connector

All user I/O is transmitted through a 68-pin connector. Refer to the 

Custom 

Cabling

 section in Chapter 1, 

Introduction

, and to Chapter 3, 

Signal 

Connections

, for additional information.

Nonvolatile RAM/DAC Control

The 6703/6704 devices have one 16-bit DAC that is time-division 

multiplexed to create all the output channels. Each channel has a 

track-and-hold circuit to maintain the channel value between DAC updates. 

On the 6703, the DAC is multiplexed to create 16 voltage outputs and two 

calibration channels. On the 6704, the DAC is multiplexed to create 

16 voltage outputs, 16 current outputs, and four calibration channels.

Data is stored in a nonvolatile RAM (nvRAM). The nvRAM/DAC control 

reads the DAC channel data stored in the nvRAM and updates the DAC 

periodically. The nvRAM/DAC control also controls the analog 

demultiplexing circuits to route the DAC output to the correct analog output 

channel. You can choose to save nvRAM data so that the current output 

values will become the power-on states.

Digital I/O Control

The 6703/6704 devices have eight digital I/O lines configured as one 8-bit 

port. You can configure each line independently as an input or output. The 

DIO lines have 16 mA of sink capability and 16 mA of source capability. 

All digital lines are TTL compatible. At power up, all digital lines are 

configured as inputs.

Temperature Sensor

The onboard temperature sensor measures the air temperature flowing over 

the board. This sensor is positioned near the onboard precision voltage 

reference, which can be affected by extreme temperatures. This sensor has 

a serial digital interface.