ATmega128 datasheet(256/386 Pages) ATMEL

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2467S–AVR–07/09

ATmega128

Scanning the Digital

Port Pins

Figure 124 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. Figure 125 shows a

simple digital Port Pin as described in the section “I/O Ports” on page 66. The Boundary-scan

details from Figure 124 replaces the dashed box in Figure 125.

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 Figure 125 to make the

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.

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

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