IDT 89HPES24N3A, User Manual

Page: 165 / 168

IDT JTAG Boundary Scan
PES24N3A User Manual 10 - 5 April 10, 2008
Notes
Figure 10.4 Diagram of Output Cell
The output enable cells are also output cells. The simplified logic is shown in Figure 10.5.
Figure 10.5 Diagram of Bidirectional Cell
The bidirectional cells are composed of only two boundary scan cells. They contain one output enable
cell and one capture cell, which contains only one register. The input to this single register is selected via a
mux that is selected by the output enable cell when EXTEST is disabled. When the Output Enable Cell is
driving a high out to the pad (which enables the pad for output) and EXTEST is disabled, the Capture Cell
will be configured to capture output data from the core to the pad.
However, in the case where the Output Enable Cell is low (signifying a tri-state condition at the pad) or
EXTEST is enabled, the Capture Cell will capture input data from the pad to the core. The configuration is
shown graphically in Figure 10.5.
Data from Core
Data from Previous Cell
shift_dr
To Next Cell
To Output Pad
clock_dr
update_dr
MU
X
D
Q
D Q
EXTEST
MUX
D Q D Q
Data from core
shift_dr
MU
X
D Q
D Q
clock_dr
shift_dr
update_dr
MUX
MU
X
MU
X
OEN to pad
I/O pin
Output enable from core
EXTEST
EXTEST
Data from previous cell
To next cell