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MEGA128CAN Datasheet, PDF (294/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER | |||
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MCU Status Register â
MCUSR
The MCU Status Register provides information on which reset source caused an MCU
reset.
Bit
7
6
5
4
3
2
1
0
â
â
â
JTRF WDRF BORF EXTRF PORF MCUSR
Read/Write
R
R
R
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
See Bit Description
⢠Bit 4 â JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register
selected by the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or
by writing a logic zero to the flag.
Boundary-scan Chain
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.
Scanning the Digital Port Pins
Figure 145 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 â PUExn
â function, and a bi-directional pin cell that combines the three signals Output Control â
OCxn, Output Data â ODxn, and Input Data â 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 146
shows a simple digital port pin as described in the section âI/O-Portsâ on page 61. The
Boundary-scan details from Figure 145 replaces the dashed box in Figure 146.
When no alternate port function is present, the Input Data â ID â 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 â DD Register, and
the Pull-up Enable â PUExn â corresponds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 146 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.
294 AT90CAN128
4250EâCANâ12/04
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