
301
7682C–AUTO–04/08
AT90CAN32/64/128
23.3.2.4
Device ID
The full Device ID is listed in
Table 23-4 following the AT90CAN32/64/128 version.
23.3.3
Reset Register
The Reset Register is a test data register used to reset the part. Since the AVR tri-states Port
Pins when reset, the Reset Register can also replace the function of the unimplemented optional
JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The part is
reset as long as there is a high value present in the Reset Register. Depending on the fuse set-
tings for the clock options, the part will remain reset for a reset time-out period (refer to “System
Clock” on page 37) after releasing the Reset Register. The output from this data register is not
latched, so the reset will take place immediately, as shown in
Figure 23-2.
Figure 23-2. Reset Register
23.3.4
Boundary-scan Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on the dig-
ital I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
off-chip connections.
23.4
Boundary-scan Specific JTAG Instructions
The instruction register is 4-bit wide, supporting up to 16 instructions. Listed below are the JTAG
instructions useful for Boundary-scan operation. Note that the optional HIGHZ instruction is not
implemented, but all outputs with tri-state capability can be set in high-impedant state by using
the AVR_RESET instruction, since the initial state for all port pins is tri-state.
As a definition in this datasheet, the LSB is shifted in and out first for all Shift Registers.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which data register is selected as path between TDI and TDO for each instruction.
Table 23-4.
Device ID
Version
JTAG Device ID (Hex)
AT90CAN32 revision B
0x0958103F
AT90CAN64 revision A
0x0968103F
AT90CAN128 revision D
0x0978103F
D
Q
From
TDI
ClockDR
AVR_RESET
To
TDO
From
Other
Internal
and
External
Reset
Sources
Internal
reset