M68HC11
REFERENCE MANUAL
RESETS AND INTERRUPTS
MOTOROLA
5-3
registers are indeterminate after reset. The output-compare 1 (OC1M) mask register
is cleared so that successful OC1 compares do not affect any I/O pins. The other four
output compares are configured to not affect any I/O pins on successful compares. All
three input-capture edge-detector circuits are configured for capture-disabled opera-
tion. The timer overflow interrupt flag and all eight timer function interrupt flags are
cleared. All nine timer interrupts are disabled since their mask bits are cleared.
5.1.1.5 Real-Time Interrupt
The real-time interrupt flag is cleared, and automatic hardware interrupts are masked.
The rate control bits are cleared after reset and may be initialized by software before
the real-time interrupt system is used.
5.1.1.6 Pulse Accumulator
The pulse accumulator system is disabled at reset so that the pulse accumulator input
(PAI) pin defaults to being a general-purpose input pin.
5.1.1.7 COP Watchdog
The computer operating properly (COP) watchdog system is enabled if the NOCOP
control bit in the CONFIG register (EEPROM cell) is clear and disabled if NOCOP is
set. The COP rate is set for the shortest duration time-out.
5.1.1.8 Serial Communications Interface (SCI)
The reset condition of the SCI system is independent of the operating mode. At reset,
the SCI baud rate is indeterminate and must be established by a software write to the
BAUD register. All transmit and receive interrupts are masked, and both the transmit-
ter and receiver are disabled so the port pins default to being general-purpose I/O
lines. The SCI frame format is initialized to an 8-bit character size. The send break and
receiver wake-up functions are disabled. The transmit data register empty (TDRE) and
transmit complete (TC) status bits in the SCI status register are both set, indicating that
there is no transmit data in either the transmit data register or the transmit serial shift
register. The receive data register full (RDRF), IDLE, overrun (OR), and framing error
(FE) receive-related status bits are all cleared. Upon reset in special bootstrap mode,
execution begins in the 192-byte bootstrap ROM, which changes some of the initial
conditions by the time the bootloading process is finished. This firmware sets port D
to wired-OR mode, establishes a baud rate, and enables the SCI receiver and trans-
mitter.
5.1.1.9 Serial Peripheral Interface (SPI)
The SPI system is disabled by reset. The port pins associated with this function default
to being general-purpose I/O lines.
5.1.1.10 Analog-to-Digital (A/D) Converter
The A/D converter system configuration is indeterminate after reset. The conversion
complete flag is cleared by reset. The A/D power-up (ADPU) bit is cleared by reset,
disabling the A/D system.