User manual

22 GR-LEON4-ITX Development Board

User Manual

2.18 Other Auxiliary Interfaces and Circuits

Oscillators and Clock Inputs

The oscillator and clock scheme for the GR-LEON4-ITX Board is shown in Figure 2-17.

The main oscillator for the GR-LEON4-ITX ASIC is a 50 MHz Crystal oscillator. This

oscillator is an SMD oscillator soldered on to the board and a zero-delay buffer circuit

(CY2305) is used to distribute this 50MHz clock signal.

Addtionally, oscillators are provided as follows:

• 33.3 MHz oscillator with zero delay buffer for PCI interface and slots

• 19.2 MHz, generates 60MHz clock for USB interfaces

• 32.768 kHz crystal for real-time clock chip with battery back-up

Internally to the ASIC, PLL circuits generate the required clock frequencies and phases as

represented in Figure 2-18 for the following:

• Processor Main frequency

• DDR2 memory clocks

• Vide Interface clocks

• IP core clocks

If a different user defined main operating frequency of the ASIC is required, this can be

achieved by installing a 4 pin DIL8 style oscillator, in socket X2 on the board and moving

jumper JP1.