XESS XSV, Manual, Page: 12 / 50

11
4
XSV Circuitry
This section describes the various sections of the XSV Board and shows how the I/O of
the FPGA and CPLD are connected to the rest of the circuitry. The schematics which
follow are less detailed so as to simplify the descriptions. Please refer to the complete
schematics at the end of this document if you need more details.
Programmable logic: XCV50-XCV800 Virtex FPGA and XC95108 CPLD
The XSV Board contains two programmable logic chips:
n A XILINX Virtex FPGA in a 240-pin QFP package. Virtex FPGAs from 57 Kgates
(XCV50) up to 888 Kgates (XCV800) are compatible with the XSV Board. The Virtex
FPGA is the main repository of programmable logic on the XSV Board.
n A XILINX XC95108 CPLD which is used to manage the configuration of the Virtex
FPGA via the parallel port, serial port, or Flash RAM. The CPLD also controls the
configuration of the Ethernet PHY chip.
100 MHz programmable oscillator
A Dallas DS1075 programmable oscillator provides a clock signal to both the FPGA and
the CPLD. The DS1075 has a maximum frequency of 100 MHz which can be divided to
provide frequencies of 100 MHz, 50 MHz, 33.3 MHz, 25 MHz, ..., 48.7 KHz. The clock
signal is connected to dedicated clock inputs of both the CPLD and FPGA as follows:
DS1075
Output
Virtex
FPGA Pin
XC95108
CPLD Pin
CLK 89 22
To set the divisor value, the DS1075 must be placed in its programming mode. This is
done by pulling the clock output to Vcc on power-up with a shunt on jumper J24. Then
programming commands to set the divisor can be sent to the DS1075 by either the CPLD
or FPGA. The divisor is stored in EEPROM in the DS1075 so it will be restored whenever
power is applied to the XSV Board.
To get a precise frequency value or to sync the XSV circuitry with an external system, you
can insert an external clock signal through connector J27. This external clock replaces the
100 MHz internal oscillator of the DS1075. The clock source is stored in EEPROM so the
DS1075 must be specifically programmed to enable or disable this option.