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LPC47B34x Board Test
Introduction
The LPC47B34x provides board test capability through the XNOR chain. When the chip is in the
XNOR chain test mode, setting the state of any of the input pins to the opposite of its current state will
cause the output of the chain to toggle.
All pins on the chip are inputs to the XNOR chain, with the exception of the following:
1. VCC (pins 19, 80, 121) and VTR (pin 15).
2. VSS (pins 6, 32, 57, 87, 99).
3. BLINK/GP31 (pin 13). This is the chain output.
4. nPCI_RESET (pin 27).
To put the chip in the XNOR chain test mode, tie LAD0 (pin 21) and nLFRAME (pin 25) low. Then
toggle nPCI_RESET (pin 27) from a low to a high state. Once the chip is put into XNOR chain test
mode, LAD0 (pin 21) and nLFRAME (pin 25) become part of the chain.
To exit the XNOR chain test mode tie LAD0 (pin 21) or nLFRAME (pin 25) high. Then toggle
nPCI_RESET (pin 27) from a low to a high state. A VCC POR will also cause the XNOR chain test
mode to be exited. To verify the test mode has been exited, observe the output on BLINK/GP31 (pin
13). Toggling any of the input pins should not cause its state to change.
Setup
Warning:
Ensure power supply is off during setup.
1. Connect VSS (pins 6, 32, 57, 87, 99) to ground.
2. Connect VCC (pins 19, 80, 121) and VTR (pin 15) to VCC (3.3V).
3. Connect an oscilloscope or voltmeter to BLINK/GP31 (pin 13).
4. All other pins should be tied to ground.
Testing
1. Turn power on.
2. With LAD0 (pin 21) and nLFRAME (pin 25) low, bring nPCI_RESET (pin 27) high. The chip
is now in XNOR chain test mode. At this point, all inputs to the XNOR chain are low. The
output on BLINK/GP31 (pin 13) should also be low. Refer to INITIAL CONFIG on Truth
Table 1.
3. Bring pin 128 high. The output on BLINK/GP31 (pin 13) should go high. Refer to STEP ONE
on Truth Table 1.
4. In descending pin order, bring each input high. The output should switch states each time an
input is toggled. Continue until all inputs are high. The output on BLINK/GP31 should now
be low. Refer to END CONFIG on Truth Table 1.
5. The current state of the chip is now represented by INITIAL CONFIG in Truth Table 2.
6. Each input should now be brought high, starting at pin one and continuing in ascending
order. Continue until all inputs are low. The output on BLINK/GP31 should now be low. Refer
to Truth Table 2.
7. To exit test mode, tie LAD0 (pin 21) or nLFRAME (pin 25) high, and toggle nPCI_RESET
from a low to a high state.