AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 293

• Manufacturer Part Number: AT90CAN128-16AE
• Description: 8-bit Avr Microcontroller With 128K Bytes of Isp Flash And CAN Controller.flash (Kbytes) 128 Vcc (V) 2.7-5.5 EEPROM (Kbytes) 4 SRAM (bytes) 4K CAN (mess. Obj.) 15
• Manufacturer: ATMEL Corporation

Boundary-scan Chain
Scanning the Digital Port Pins
4250C–CAN–03/04
The Boundary-scan chain has the capability of driving and observing the logic levels on
the digital I/O pins, as well as the boundary between digital and analog logic for analog
circuitry having off-chip connection.
Figure 142 shows the Boundary-scan Cell for a bi-directional port pin with pull-up func-
tion. 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 datasheet. Figure 143
shows a simple digital port pin as described in the section “I/O-Ports” on page 62. The
Boundary-scan details from Figure 142 replaces the dashed box in Figure 143.
When no alternate port function is present, the Input Data – ID – corresponds to the
PINxn Register 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 – corresponds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 143 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 digital logic and the analog circuitry.
Figure 142. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function.
Pullup Enable (PUE)
Output Control (OC)
Output Data (OD)
Input Data (ID)
0
1
From Last Cell
0
1
0
1
0
1
ShiftDR
ClockDR
D
D
D
FF2
FF1
FF0
To Next Cell
Q
Q
Q
UpdateDR
D
G
D
G
D
G
LD2
LD1
LD0
Q
Q
Q
0
1
0
1
0
1
AT90CAN128
EXTEST
Vcc
293