IDT EB4T4 Eval Board, Руководство пользователя

Страница: 12 / 42

IDT Installation of the EB4T4 Eval Board
EB4T4 Eval Board Manual 2 - 2 August 20, 2007
Notes
The source for the onboard clock is the ICS9FG104 clock generator device (U8) connected to a 25MHz
oscillator (Y1). When using the onboard clock generator, the EB4T4 allows the selection of spread spec-
trum settings via DIP switches as described in Table 2.2 . Spread Spectrum technology reduces peak EMI
emissions by modulating the frequency to spread the peak energy over a wider bandwidth.
If the Clock Spread Spectrum is used to modulate data rate, then both ports must use same modulated
clock source. Therefore, if your system uses SSC, the on-board clock generator must be disabled and the
upstream reference clock should be used instead.
The output of the onboard clock generator is accessible through two SMA connectors located on the
Evaluation Board. See Table 2.3. This can be used to connect a scope for probing or capturing purposes
and cannot be used to drive the clock from an external source.
Figure 2.1 illustrates the clock distribution block diagram for the EB4T4 evaluation board.
Figure 2.1 Clock Distribution Block Diagram
Clock Spread Spectrum Switch - S3[2]
S3[2] Spread Spectrum
OFF Enable Spread Spectrum
ON Disable Spread Spectrum (Default)
Table 2.2 Spread Spectrum Clock Selection
Onboard Reference Clock Output (Differential) – J3, J1
J3 Positive Reference Clock
J1 Negative Reference Clock
Table 2.3 SMA Connectors - Onboard Reference Clock
PEREFCLK0
PEREFCLK1
Port2
Port3
Port4
Upstream PEREFCLK
25MHz
ICS9DB803D
SMA - J1
SMA - J3
ISC9FG104
Resistor Switch