National Instruments PXIe-6674, Руководство пользователя

Страница: 14 / 30

Table 5. Combinations of PFI Lines for PFI_LVDS
PFI Lines PFI_LVDS Lines
PFI 0 PFI_LVDS 0 Negative
PFI 1 PFI_LVDS 0 Positive
PFI 2 PFI_LVDS 1 Negative
PFI 3 PFI_LVDS 1 Positive
PFI 4 PFI_LVDS 2 Negative
PFI 5 PFI_LVDS 2 Positive
Each of the three PFI_LVDS can be enabled for LVDS operation or used for two single ended
PFIs. When enabled for LVDS operation, the PFI_LVDS pair can be configured as either an
input or an output. PFI_LVDS lines can not be used as an input and output at the same time.
Because of the increased speed capabilities, the PFI_LVDS include additional routing
capabilities not offered with the single ended PFI. When used as an input, the PFI_LVDS
signal goes to the FPGA for trigger routing. When used as an output, the PFI_LVDS can be
sourced from the FPGA for trigger usage, or from either the PXI_DSTARA or high speed
CLKOUT outputs.
If the PFI_LVDS output is used for trigger routing, it is sourced from the FPGA and has all the
same trigger routing characteristics as other trigger destinations. Refer to the
Using the Front
Panel PFIs for LVDS Triggers section for details on using PFI_LVDS for sending and
receiving trigger signals.
CLKOUT
The CLKOUT SMA connector on the front panel provides a means to export a clock signal
from the PXIe-6674 to an external device or another system timing module. The CLKOUT
driver uses two separate circuits for driving CLKOUT, one for low speed frequencies (50 MHz
and below) and one for high speed (above 50 MHz). The low speed driver uses 5 V CMOS
logic with source impedance of 50 Ω and is AC coupled. The high speed driver produces an
800 mv
pp
swing into a 50 Ω load and is also AC coupled.
The sources available to be routed to CLKOUT differ depending on whether the low speed or
high speed driver is used. The sources available to the low speed driver are PXI_CLK10 and
Clock Generation for generated frequencies 50 MHz and below. Sources available to the high
speed CLKOUT are Clock Generation and PXIe_DSTARA.
NI-Sync software will select the low speed or high speed driver automatically based on the
source connected to CLKOUT.
Routing Trigger Signals
The PXIe-6674 has versatile trigger routing capabilities. It can route signals to and from the
front panel, the PXI_STAR trigger, the PXI_TRIG triggers, and PXIe_DSTARB/
PXIe_DSTARC.
14 | ni.com | PXIe-6674 User Manual