
NI Digital System Development Board User Manual
|
© National Instruments
|
39
Clock Sources
The DSDB provides a 50 MHz clock to the Zynq PS_CLK input, which is used to generate the
clocks for each of the PS subsystems. The 50 MHz input allows the processor to operate at a
maximum frequency of 650 MHz and the DDR3 memory controller to operate at a maximum of
525 MHz (1050 Mbps).
The PS has a dedicated PLL capable of generating up to four reference clocks, each with settable
frequencies, that can be used to clock custom logic implemented in the PL. Additionally, The
DSDB provides an external 125 MHz reference clock directly to pin L18 of the PL. The external
reference clock allows the PL to be used completely independently of the PS, which can be
useful for simple applications that do not require the processor.
The PL of the Zynq-Z7020 also includes 4 MMCMs and 4 PLLs that can be used to generate
clocks with precise frequencies and phase relationships. Any of the four PS reference clocks or
the 125 MHz external reference clock can be used as an input to the MMCMs and PLLs. For a
full description of the capabilities of the Zynq PL clocking resources, refer to the
Series FPGAs
Clocking Resources User Guide
, available from Xilinx.
Note that the reference clock output from the Ethernet PHY is used as the 125 MHz reference
clock to the PL, in order to cut the cost of including a dedicated oscillator for this purpose. Keep
in mind that CLK125 will be disabled when the Ethernet PHY (IC1) is held in hardware reset by
driving the PHYRSTB signal low.
Basic I/O
The DSDB includes a four-digit seven segment display, eight slide switches, four push buttons,
and eight individual LEDs connected to the Zynq PL. There is also one LED connected directly
to the PS via MIO pin 7. The push buttons and slide switches are connected to the Zynq via series
resistors to prevent damage from inadvertent short circuits (a short circuit could occur if a pin
assigned to a push button or slide switch was inadvertently defined as an output). The push
buttons are “momentary” switches that normally generate a low output when they are at rest, and
a high output only when they are pressed. Slide switches generate constant high or low inputs
depending on their position.
The eight high-efficiency LEDs are anode-connected to the Zynq via 330-
resistors, so they
will turn on when a logic high voltage is applied to their respective I/O pin. Additional LEDs
that are not user-accessible indicate power-on (PGOOD), FPGA programming status (DONE),
and USB and Ethernet port status.
The LED attached directly to the PS are accessed using the Zynq GPIO controller. This core is
described in full in Chapter 14 of the
Zynq Technical Reference Manual
.