| Reset and preset pins on devices under test should be able to be
independently controlled. |
| Initialization of LSI, VLSI, and ASIC devices to a known stable condition
is essential for accurate, reliable testing and fault diagnosis. All control inputs, of
devices under test, should be isolated if unused, by pullup or pulldown resistors for
effective device testing by the software algorithms. DO NOT tie unused
control lines directly to a voltage or ground. |
| Outputs of devices in a sequential circuit may need to be set or cleared
to a condition that is different from that chosen for initialization. Control lines should
not be tied directly to voltages or ground. All control inputs of sequential devices must
be accessible independently, via unique and separate pullup and pulldown resistors. To
permit use of device models resident in the ATE libraries, device control and enable lines
must be free to change state. All device control inputs on a single device or functionally
interdependent devices must be accessible and settable independently via unique and
separate pullup and pulldown resistors. |
| To avoid conflict between the in circuit ATE program and internally
generated instructions, the microprocessor must be fully controllable during in-circuit
test. All unused microprocessor control lines must be accessible and settable
independently using separate pullup and pulldown resistors. Use gates, tri-statable
buffers, and jumpers to disable clocks. |
| During test, it may become necessary to backdrive device outputs low when
they would ordinarily be in a high state. Some devices may require high currents to draw
the outputs to stable lows. For tri-statable devices this can be avoided if the tri-state
mode can be enabled. All functionally interdependent tri-statable devices must be capable
of being tri-stated independently.
When applicable, use components with tri-statable outputs. |
| To avoid untestable conditions in series circuits, control and enable
lines tied to pullups and pulldowns must not be tied to control and enable lines of other
devices. The tester must have complete and independent control of devices in series. |
|
