61
AT94KAL Series FPSLIC
Rev. 1138G–FPSLI–11/03
Reset Sources
The embedded AVR core has five sources of reset:
•
External Reset. The MCU is reset immediately when a low-level is present on the RESET
or AVR RESET pin.
•
Power-on Reset. The MCU is reset upon chip power-up and remains in reset until the
FPGA configuration has entered Idle mode.
•
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
watchdog is enabled.
•
Software Reset. The MCU is reset when the SRST bit in the Software Control register is
set (one).
•
JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset Register,
one of the scan chains of the JTAG system. See “IEEE 1149.1 (JTAG) Boundary-scan” on
page 73.
During reset, all I/O registers except the MCU Status register are then set to their Initial Val-
ues, and the program starts execution from address $0000. The instruction placed in address
$0000 must be a JMP – absolute jump instruction to the reset handling routine. If the program
never enables an interrupt source, the interrupt vectors are not used, and regular program
code can be placed at these locations. The circuit diagram in Figure 35 shows the reset logic.
Table 16 defines the timing and electrical parameters of the reset circuitry.
Figure 35.
Reset Logic
MCU STATUS
DATA BUS
RESET/
AVR RESET
WATCHDOG
TIMER
INTERNAL
OSCILLATOR
SYSTEM
CLOCK
DELAY COUNTERS
Q
S
R
INTERNAL
RESET
POR
COUNTER RESET
SEL [4:0] CONTROLLED
BY FPGA CONFIGURATION
FULL
FPGA
CONFIG
LOGIC
EXTRF
WDRF
SFTCR
BIT 0
PORF
JTAG RESET
REGISTER
JT RF