Specifications

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