82801DB Datasheet, PDF (552/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Testability
19.2
Tri-State Mode
When in the tri-state mode, all outputs and bi-directional pin are tri-stated, including the XOR
chain outputs.
19.3 XOR Chain Mode
In the ICH4, provisions for Automated Test Equipment (ATE) board level testing are implemented
with XOR chains. The ICH4 signals are grouped into four independent XOR chains which are
enabled individually. When an XOR chain is enabled, all output and bi-directional buffers within
that chain are tri-stated, except for the XOR chain output. Every signal in the enabled XOR chain
(except for the XOR chain’s output) functions as an input. All output and bi-directional buffers for
pins not in the selected XOR chain are tri-stated. Figure 19-2 is a schematic example of XOR chain
circuitry.
Figure 19-2. Example XOR Chain Circuitry
Vcc
Input
Pin 1
Input
Pin 2
Input
Pin 3
Input
Pin 4
Input
Pin 5
Input
Pin 6
XOR
Chain
Output
19.3.1 XOR Chain Testability Algorithm Example
XOR chain testing allows motherboard manufacturers to check component connectivity
(e.g., opens and shorts to VCC or GND). An example algorithm to do this is shown in Table 19-2.
Table 19-2. XOR Test Pattern Example
Vector
1
2
3
4
5
6
7
Input
Pin 1
0
1
1
1
1
1
1
Input
Pin 2
0
0
1
1
1
1
1
Input
Pin 3
0
0
0
1
1
1
1
Input
Pin 4
0
0
0
0
1
1
1
Input
Pin 5
0
0
0
0
0
1
1
Input
Pin 6
0
0
0
0
0
0
1
XOR
Output
1
0
1
0
1
0
1
In this example, Vector 1 applies all 0s to the chain inputs. The outputs being non-inverting, will
consistently produce a 1 at the XOR output on a good board. One short to VCC (or open floating to
VCC) will result in a 0 at the chain output, signaling a defect.
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Intel^® 82801DB ICH4 Datasheet