Freescale Semiconductor, Inc.
5.2.1 Central Processing Unit
After reset, the CPU fetches the reset vector from the appropriate address during the
first three cycles, and begins executing instructions. The stack pointer and other CPU
registers are indeterminate immediately after reset; however, the X and I interrupt
mask bits in the condition code register (CCR) are set to mask any interrupt requests.
Also, the S bit in the CCR is set to inhibit the STOP mode.
5.2.2 Memory Map
After reset, the INIT register is initialized to $01, putting the 1024 bytes of RAM at lo-
cations $0000 through $03FF, and the control registers at locations $1000 through
$105F. The EE[3:0] bits in the CONFIG register control the location of the 512-byte
EEPROM array.
5.2.3 Parallel I/O
When a reset occurs in expanded operating modes, port B, C, and F pins used for par-
allel I/O are dedicated to the expansion bus. If a reset occurs during a single-chip op-
erating mode, all ports are configured as general-purpose high-impedance inputs.
NOTE
Do not confuse pin function with the electrical state of the pin at reset.
All general-purpose I/O pins configured as inputs at reset are in a
high-impedance state. Port data registers reflect the port's functional
state at reset. The pin function is mode dependent.
5.2.4 Timer
During reset, the timer system is initialized to a count of $0000. The prescaler bits are
cleared, and all output compare registers are initialized to $FFFF. All input capture reg-
isters are indeterminate after reset. The output compare 1 mask (OC1M) register is
cleared so that successful OC1 compares do not affect any I/O pins. The other four
output compares are configured so that they do not affect any I/O pins on successful
compares. All input capture edge-detector circuits are configured for capture disabled
operation. The timer overflow interrupt flag and all eight timer function interrupt flags
are cleared. All nine timer interrupts are disabled because their mask bits have been
cleared.
The I4/O5 bit in the PACTL register is cleared to configure the I4/O5 function as OC5;
however, the OM5–OL5 control bits in the TCTL1 register are clear so OC5 does not
control the PA3 pin.
5.2.5 Real-Time Interrupt (RTI)
The real-time interrupt flag (RTIF) is cleared and automatic hardware interrupts are
masked. The rate control bits are cleared after reset and can be initialized by software
before the real-time interrupt (RTI) system is used.
RESETS AND INTERRUPTS
TECHNICAL DATA
5-5
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