LPC47M172 SMSC Corporation, LPC47M172 Datasheet - Page 225

• Manufacturer Part Number: LPC47M172
• Description: ADVANCED I/O CONTROLLER WITH MOTHERBOARD GLUE LOGIC
• Manufacturer: SMSC Corporation

Chapter 15 Board Test Mode
SMSC LPC47M172
Board level testing is implemented with an XOR Chain. The XOR chain testing allows motherboard
manufacturers to check component connectivity (e.g., opens and shorts to VCC or GND).
The TEST_EN pin is used as a strap pin to enter test mode. This pin has an internal 30 µA pull-down
resistor to VSS. An external 10 kohm pull-up to V_3P3_STBY is used to put the device in test mode.
Both VCC and VTR supplies are required for the device to operate properly in test mode.
The part enters board test (XOR-chain) mode when the TEST_EN pin is brought high. The part remains in
test mode while TEST_EN is high. Bringing TEST_EN low will exit test mode.
When the XOR chain is entered, all output and bi-directional buffers within that chain are tri-stated, except
for the XOR chain output. Every signal in the XOR chain (except for the XOR chain’s output) functions as
an input. Figure 15.1 is a schematic example of XOR chain circuitry.
The XOR chain output is on pin 30, nDTR1/XOR.
The input pin ordering is as follows: the first input pin in the XOR chain is pin 1 of the chip (MCLK), and the
order continues around the chip in increasing pin number order to end at pin 128, skipping those pins that
are excluded from the chain.
The following pins are excluded from the XOR chain.
The total number of pins excluded from the XOR chain is 23; therefore there are an odd number of pins in
the XOR chain.
nRSMRST pin (1)
REF5V pin (1)
REF5V_STBY pin (1)
VCC pins (5)
VTR pins (4)
V_5P0_STBY pin (1)
VSS pins (7)
F_CAP pin (1)
nDTR1/XOR pin (1)
TEST_EN pin (1)
VCC3
Pin 1
Input
Pin 2
Input
Figure 15.1 - Example XOR Chain Circuitry
DATASHEET
Pin 3
Input
Page 225
Input
Pin 4
Pin 5
Input
Advanced I/O Controller with Motherboard GLUE Logic
SMSC/Non-SMSC Register Sets (Rev. 02-27-04)
XOR Chain
Output
Datasheet