Datasheet

306
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
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 28-4 on page 307
to make the scan chain read the actual pin value. For analog function, there is a direct connec-
tion from the external pin to the analog circuit. There is no scan chain on the interface between
the digital and the analog circuitry, but some digital control signal to analog circuitry are turned
off to avoid driving contention on the pads.
When JTAG IR contains EXTEST or SAMPLE_PRELOAD the clock is not sent out on the port
pins even if the CKOUT fuse is programmed. Even though the clock is output when the JTAG IR
contains SAMPLE_PRELOAD, the clock is not sampled by the boundary scan.
Figure 28-3. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function.
DQ DQ
G
0
1
0
1
DQ DQ
G
0
1
0
1
0
1
Port Pin (PXn)
Vcc
EXTEST
To Next Cell
ShiftDR
Output Control (OC)
Output Data (OD)
Input Data (ID)
From Last Cell
UpdateDRClockDR
FF1 LD1
LD0FF0
0
1
Pull-up Enable (PUE)