41978 AMD RS690M Databook 3.06
© 2008 Advanced Micro Devices, Inc.
7-2
Proprietary
XOR Tree
Figure 7-1 An Example of a Generic XOR Tree
Pin A is assigned to the output direction, and pins 1 through 6 are assigned to the input direction. It can be seen that after
all pins 1 to 6 are assigned to logic 0 or 1, a logic change in any one of these pins will toggle the output pin A.
The following is the truth table for the XOR tree shown in
The XOR start signal is assumed to be logic 1.
7.3.2
Description of the XOR Tree for the RS690M
The XOR start signal is applied at the TDI pin of the JTAG circuitry and the output of the XOR tree is obtained at the
TDO pin. Refer to
for the list of the signals included on the XOR tree. There is no specific connection order
to the signals on the tree. A toggle of any of these balls in the XOR tree will cause the output to toggle.
7.3.3
XOR Tree Activation
The RS690M chip enters the XOR tree test mode by means of the JTAG. First, the 8-bit instruction register of the JTAG
is loaded with the XOR instruction (“00001000”). This instruction assigns the input direction to all the pins except pin
TDO, which is assigned the output direction to serve as the output of the XOR tree. After loading, the JTAG is taken to
the Run-Test state for completion of the XOR tree initialization.
Note:
10MHz clock frequency is recommended for the XOR TREE test mode.
7.3.4
XOR Chain for the RS690M/RS690T
When the XOR tree is activated, any pin on the XOR tree must be either pulled down or pulled up to the I/O voltage of the
pin. Only pins that are
not
on the XOR tree can be left floating.
When differential signal pairs are listed as single entries on the XOR tree, opposite input values should be applied to the
two signals in each pair (e.g., for entry no. 13 on the tree, when “1” is applied to HT_RXCAD15P, “0” should be applied
to HT_RXCAD15N).
XOR Start Signal
1
2
3
4
5
6
A
Table 7-2 Example of an XOR Tree
Test Vector
number
Input Pin 1
Input Pin 2
Input Pin 3
Input Pin 4
Input Pin 5
Input Pin 6
Output Pin A
1
0
0
0
0
0
0
1
2
1
0
0
0
0
0
0
3
1
1
0
0
0
0
1
4
1
1
1
0
0
0
0
5
1
1
1
1
0
0
1
6
1
1
1
1
1
0
0
7
1
1
1
1
1
1
1