Excalibur Excalibur EPXA1, Hardware Reference Manual

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Altera Corporation 27
EPXA1 Development Board Hardware Reference Manual
By selecting the position of jumpers CLKA Select and CLKB Select, as
shown in
Table 17 , either the SMA connector or an alternative 5-V DIL14
oscillator can be used instead of the 25-MHz on-board oscillator. To use
the SMA connector to drive a clock onto the board from an external
source, the alternative 5-V DIL14 oscillator socket must not contain an
oscillator. To use an alternative 5-V DIL14 oscillator, ensure that no clock
is attached to the SMA connector .
Sources for the Stripe Clock Reference
There are three options for providing a source for the EPXA1 embedded
stripe clock reference,
CLK_REF
:
■
25-MHz on-board oscillator
■
SMA connector
■
Alternative 5-V DIL14 oscillator
Using the 25-MHz On-board Oscillator
To use the 25-MHz on-board oscillator, set CLKA Select to position 1-2 to
select it.
Using the SMA Connector
To select the SMA connector, follow the steps below:
1. Remove any alternative 5-V DIL14 oscillator from the socket, XSKT1.
2. Apply an external clock source to the SMA connector.
The clock signal should be a maximum 5 V
PP
.
3. Set CLKA Select to position 2-3.
Table 17. CLKA Select & CLKB Select Jumper Settings
Pin 1-2 Connected Pin 2-3 Connected
CLKA
Select 25-MHz on-board oscillator provides a clock to
CLK_REF
, EPXA1 dedicated inputs
CLK1
and
CLK2
, and both expansion headers
Alternative 5-V DIL14 oscillator or SMA connector
selected provides
CLK_REF
, EPXA1 dedicated
inputs
CLK1
and
CLK2
, and both expansion
headers
CLKB
Select 25-MHz on-board oscillator provides the clock to
EPXA1 dedicated inputs
CLK3
and
CLK4
Alternative 5-V DIL14 oscillator or SMA connector
provides the clock to EPXA1 dedicated inputs
CLK3
and
CLK4