256
2467S–AVR–07/09
ATmega128
Scanning the Digital
Port Pins
shows the Boundary-scan Cell for a bi-directional port pin with pull-up function. The
cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn – function, and a
bi-directional pin cell that combines the three signals Output Control – OCxn, Output Data –
ODxn, and Input Data – IDxn, into only a two-stage Shift Register. The port and pin indexes are
not used in the following description
The Boundary-scan logic is not included in the figures in the Data Sheet.
shows a
simple digital Port Pin as described in the section
. The Boundary-scan
details from
replaces the dashed box in
When no alternate port function is present, the Input Data – ID corresponds to the PINxn Regis-
ter value (but ID has no synchronizer), Output Data corresponds to the PORT Register, Output
Control corresponds to the Data Direction – DD Register, and the Pull-up Enable – PUExn – cor-
responds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in
scan chain read the actual pin value. For Analog function, there is a direct connection from the
external pin to the analog circuit, and a scan chain is inserted on the interface between the digi-
tal logic and the analog circuitry.
Figure 124.
Boundary-scan Cell for Bi-directional Port Pin with Pull-Up Function.
D
Q
D
Q
G
0
1
0
1
D
Q
D
Q
G
0
1
0
1
0
1
0
1
D
Q
D
Q
G
0
1
Port Pin (PXn)
Vcc
EXTEST
To Next Cell
ShiftDR
Output Control (OC)
Pullup Enable (PUE)
Output Data (OD)
Input Data (ID)
From Last Cell
UpdateDR
ClockDR
FF2
LD2
FF1
LD1
LD0
FF0
