Create a PCB and Test Fixture

Before starting test development, the first step to successful in-system programming

is the proper layout of the board and the subsequent creation of the test fixture.

Creating the PCB

The following recommendations highlight important areas of PCB design issues:

■ The TCK signal trace should be treated as carefully as a clock tree. TCK is the clock

for the entire Joint Test Action Group (JTAG) chain of devices. These devices are

edge-triggered on the TCK signal, so it is imperative that this signal be protected

from high-frequency noise and have good signal integrity. Ensure that the signal

meets the tR and tF parameters specified in the device data sheet.

■ Add a pull-down resistor to TCK. The TCK signal should be held low through a

pull-down resistor in-between PCF downloads. For more information about

pattern capture format (PCF) downloads, refer to “Step 2: Create a Serial Vector

Format File”. You should hold TCK low because the Agilent 3070 drivers go into a

“high-Z” state in-between tests and briefly drive low as the next PCF is applied.

When the TCK line “floats”, the programming data stream is corrupted and the

device is not programmed correctly.

■ Provide VCC and GND test access points for the nails of the test fixture. During

operation, there should be enough access points to allow quiet PCB operation.

Having too few access points results in a noisy system that can disrupt JTAG

scans.

■ Turn off on-board oscillators. During programming, on-board oscillators should

have the ability to be electrically turned off to reduce system noise.

■ Add external resistors to pull outputs to a defined logic level during

programming.

1 Output pins are tri-stated during programming and are pulled up by a weak internal

resistor. However, Altera recommends that signals requiring a pre-defined level be

externally forced to the appropriate level using an external resistor.

f For more information about board design for ISP, refer to the In-System

Programmability Guidelines for MAX II Devices chapter in the MAX II Device Handbook.

Creating the Fixture

Providing a clean interface between the test fixture and the target board is essential for

successful in-system programming. To provide a clean interface, use short wires in the

test fixture to improve the TCK connection. Longer wires can introduce inductive

noise into the system, which can disrupt programming. The wire connecting TCK

should be no longer than 1 inch. Use the Agilent Fixture Consultant to manage the

layout and creation of the test fixture (see the Agilent Board Test Family Manual).