National Instruments Data Acquisition Device NI USB-621x, Руководство пользователя

Страница: 52 / 185

Chapter 4 Analog Input
© National Instruments Corporation 4-19 NI USB-621x User Manual
Figure 4-13. AI Sample Clock and AI Convert Clock Properly Matched
A single external signal can drive both AI Sample Clock and AI Convert
Clock at the same time. In this mode, each tick of the external clock ca
u ses
a conversion on the ADC. Fig u re 4-14 shows this timing relationship.
Figure 4-14. Single External Signal Driving AI Sample Clock and
AI Convert Clock Simultaneously
AI Convert Clock Timebase Signal
The AI Convert Clock Timebase (ai/ConvertClockTimebase) signal is
divided down to provide one of the possible so
u rces for AI Convert Clock.
Use one of the following signals as the so u rce of AI Convert Clock
Timebase:
• AI Sample Clock Timebase
• 20 MHz Timebase
AI Convert Clock Timebase is not available as an o u tp u t on the
I/O connector.
AI Hold Complete Event Signal
The AI Hold Complete Event (ai/HoldCompleteEvent) signal generates a
p
u lse after each A/D conversion begins. Yo u can ro u te AI Hold Complete
Event o u t to any o u tp u t PFI terminal.
AI Sa mple Clock
AI Convert Clock
Sa mple #1 Sa mple #2 Sa mple # 3
Ch a nnel Me asu red 1 2 3 0 1 2 3 0 1 2 3 0
AI Sa mple Clock
AI Convert Clock
Sa mple #1 Sa mple #2 Sa mple # 3
1 2 3 0 1 2 3 0 1 … 0
Ch a nnel Me asu red