PXI Timing, Triggering, and Synchronization Capabilities of E-Series Multifunction Data Acquisition Boards (NI PXI-60xxE)

Overview

This document details how National Instruments PXI-60xxE, (E-Series) multifunction data acquisition boards can share timing, triggering, and synchronization signals onto the PXI backplane. This document assumes that the reader is already familiar with general concepts of the PXI specification such as the trigger bus, star trigger, 10 MHz system reference clock, and local bus. If you are not familiar with these concepts, then you may find it beneficial to read the PXI Specification Tutorial before continuing. This document also assumes that the reader has a basic understanding of the analog input/output, digital input/output, and counter/timer features of E-series data acquisition boards. If you are not familiar with the general operation and use of these boards, then please refer to E-Series user manual, as well as the online help supplied with the NI-DAQ driver, for information on basic use of the E-Series DAQ cards.

Line Mapping to the PXI Backplane
Synchronization of National Instruments E-Series cards is accomplished with RTSI. RTSI, or Real Time Signal Integration, was originally developed as a method of synchronizing multiple PCI and ISA cards before the PXI specification was adopted in 1997. With RTSI, multiple PCI and ISA E-Series cards could be synchronized by connection of a RTSI ribbon-cable. As a result, once the PXI specification was adopted in 1997, National Instruments was able to simply tie these RTSI signals directly to the PXI backplane to extend this same synchronization functionality into PXI. Therefore, all E-Series cards (PCI, ISA, PXI) implement synchronization using the RTSI bus, and code that takes advantage of the RTSI bus is interchangeable between PCI, ISA, and PXI cards. This provides the programmer a scalable solution. For example, you can write code to test a synchronization scheme with two PCI E-Series boards in a desktop computer. Then later, you can reuse the same code to synchronize 17 PXI E-Series boards in a single chassis.

Figure 1. On PCI E-Series boards (bottom), multi-board synchronization is implemented using the RTSI connector. For PXI E-series boards (top), the RTSI connector is not needed, as these same RTSI signals are directly mapped to the PXI Backplane through the J2 connector.

From this point forward, this document will refer to the lines tied to the PXI backplane as “RTSI”. This is consistent with existing documentation and example code for the E-series data acquisition boards, which refers to these lines as “RTSIx”. However, Table I below shows how these RTSI lines directly map to the PXI backplane for integration with any industry-standard PXI capable of communicating with the indicated PXI backplane lines.

Table I. Mapping of RTSI lines to PXI Backplane Lines

60xxE	PXI Backplane
RTSI_0	PXI_Trig0
RTSI_1	PXI_Trig1
RTSI_2	PXI_Trig2
RTSI_3	PXI_Trig3
RTSI_4	PXI_Trig4
RTSI_5	PXI_Trig5
RTSI_6	PXI_Star
RTSI_CLK	PXI_Trig7

Source: PXI E-Series User Manual

Note that all but one of the RTSI lines map to the PXI Trigger Bus. RTSI6 is an exception, and is mapped to the PXI_Star line to allow the PXI E-Series boards to receive star triggers. For more information on the PXI backplane lines, refer directly to the PXI Specification, available at www.pxisa.org.

Signal Mapping to the PXI Backplane

Now that we have established how the E-Series RTSI lines map to the PXI backplane, we must next understand how real signals, such as triggers and clocks, are mapped to and from these RTSI lines. Table II below summarizes the signals that can be mapped to and from RTSI, and therefore, the PXI backplane.

Table II. PXI NI-60xxE Signals That Can Be Mapped to PXI Backplane

Signal	Drive PXI	Receive	Drive	Receive
	Trigger	PXI Trigger	PXI Star	PXI Star
	(RTSI0::5, RTSI CLK)	(RTSI0::5, RTSI CLK)	(RTSI6)	(RTSI6)
AI Start Trigger	x	x		x
AI Stop Trigger	x	x		x
AI Convert	x	x		x
AO Update	x	x		x
AI Scan Start	x	x		x
GPCTR0 Source	x	x		x
GPCTR0 Gate	x	x		x
GPCTR0 Out	x	x		x
AI Scan Clock Gate	x	x		x
AI Scan Clock		x		x
AI Clock Source		x		x
AI Clock Timebase		x		x
AO Timebase Source		x		x
AO Clock Source		x		x

Star Trigger Capability
The PXI E-series data acquisition boards do not possess the ability to drive the star trigger lines as a star trigger controller in slot 2 of PXI chassis. In slot 2 of a PXI chassis, the PXI E-Series data acquisition boards function as if they are in any generic PXI peripheral slot.

PXI System Reference Clock
The PXI E-Series Data Acquisition boards are not capable of referencing the 10 MHz system reference clock. However, a scan clock can be shared over the PXI Trigger Bus (see Table II), which provides the ability to synchronize scan clocks over the PXI Trigger Bus.

Implementation of Signal Routing using NI-DAQ 6.x
Signal routing to the PXI backplane is implemented programmatically using functions in the National Instruments Data Acquisition Driver (NI-DAQ). Functions that reference mapping to/from RTSI lines include AI Start, AI Clock Config, AI Trigger Config, AO Start, AO Clock Config, AO Trigger and Gate Config, and Route Signal. For specific details on use and parameters, please refer to the online help which installs with the NI-DAQ driver. For LabVIEW, select the menu "Help >> VI, Function, & How To Help" to access the online help.

Common Applications and Examples
Since both PXI and PCI/ISA E-series data acquisition cards implement RTSI, the software code and examples are the same for PXI and PCI/ISA for these boards. Example programs showing synchronization of multiple E-series data acquisition boards ship with the NI-DAQ driver. From LabVIEW, these examples are available directly in LabVIEW help (LabVIEW version 6.1 with NI-DAQ version 6.9.2 shown). Additionally, examples are installed for other Application Development Environments such as LabWindows/CVI, C, and Visual Basic, and are available in the NI-DAQ installation directory.


[+] Enlarge Image
Figure 2. Example programs are included with LabVIEW and the NI-DAQ driver. Selecting "Help >> Find Examples >> Hardware Input and Output >> DAQ" will lead you to the appropriate set of example programs.

Reader Comments | Submit a comment »