User Manual

the 7 Series FPGAs Clocking Resources User Guide
(https://www.xilinx.com/support/documentation/user_guides/ug472_7Series_Clocking.pdf) available from Xilinx.
Xilinx offers the Clocking Wizard IP core to assist in integrating the MMCM's and PLL's into a design. This wizard will properly
instantiate the needed MMCMs and PLLs based on the desired frequencies and phase relationships specified by the user. The wizard will
then output an easy-to-use wrapper component around these clocking resources that can be inserted into the user’s design. The clocking
wizard can be accessed from within the Vivado and IP Integrator tools.
Figure 5.1 outlines the clocking scheme used on the Eclypse Z7. Note that the reference clock output from the Ethernet PHY is used as
the 125 MHz (Megahertz (million times per second)) 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 is held in hardware reset by driving the PHYRSTB
signal low.
The Eclypse Z7 provides several different methods of resetting the Zynq-7000 device, as described in the following sections:
The Zynq PS supports external power-on reset signals. The power-on reset is the master reset of the entire chip. This signal resets every
register in the device capable of being reset. The Eclypse Z7 drives this signal from the VCC4V3 supply, the final non-adjustable supply
to be brought up in the power-on sequence, in order to hold the system in reset until all power supplies are valid. A push-button, labeled
BTNP, can be used to toggle the power-on reset signal. BTNP is located on the underside of the Eclypse Z7, below the SD card slot.
The external system reset button, labeled BTNR, resets the Zynq device without disturbing the debug environment. For example, the
previous break points set by the user remain valid after system reset. Due to security concerns, system reset erases all memory content
within the PS, including the On-Chip-Memory (OCM). The PL is also cleared during a system reset. System reset does not cause the
boot mode strapping pins to be re-sampled. After changing the boot mode jumper a power cycle is needed to act on the new setting.
BTNR is located on the underside of the Eclypse Z7, below the SD card slot.
6. Reset Sources
6.1. Power-on Reset
6.2. Processor Subsystem Reset
7.
USB-UART Bridge (Serial Port)
The Eclypse Z7 includes an FTDI FT2232HQ USB-UART bridge (attached to connector J6) that lets PC applications communicate with
the board using standard COM port commands (or the tty interface in Linux). Drivers are automatically installed in Windows and newer
versions of Linux when the Eclypse Z7 is attached. Serial port data is exchanged with the Zynq using a two-wire serial port
(TXD/RXD). After the drivers are installed, I/O commands can be used from the PC directed to the COM port to produce serial data
traffic on the Zynq pins. The port is tied to PS (MIO) pins and can be used in combination with the UART 0 controller.
The Zynq presets file (available in the Eclypse Z7 Resource Center takes care of mapping the correct MIO pins to the UART 0 controller
and uses the following default protocol parameters: 115200 baud rate, 1 stop bit, no parity, 8-bit character length.
Two status LEDs provide visual feedback on traffic flowing through the port: the transmit LED (Light Emitting Diode) (the lower of the
two yellow LEDs in the circuit board indicator, LD4) and the receive LED (Light Emitting Diode) (the upper of the two yellow LEDs in
the circuit board indicator, LD4). Signal names that imply direction are from the point-of-view of the DTE (Data Terminal Equipment),
in this case the PC.
The FT2232HQ is also used as the controller for the Digilent USB-JTAG circuitry, but the USB-UART and USB-JTAG functions behave
entirely independent of one another. Programmers interested in using the UART functionality of the FT2232 within their design do not
need to worry about the JTAG circuitry interfering with the UART data transfers, and vice-versa. The combination of these two features
into a single device allows the Zybo Z7 to be programmed and communicated with via UART from a computer attached with a single
Micro USB cable.
The connections between the FT2232HQ and the Zynq-7000 are shown in Figure 7.1.
8. Zmod Ports