Datasheet

Monitor ROM (MON)
Functional Description
MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
MOTOROLA Monitor ROM (MON) 121
NON-DISCLOSURE AGREEMENT REQUIRED
9.4.3 Data Format
Communication with the monitor ROM is in standard non-return-to-zero
(NRZ) mark/space data format. Transmit and receive baud rates must
be identical.
Figure 9-5. Monitor Data Format
9.4.4 Break Signal
A start bit (logic 0) followed by nine logic 0 bits is a break signal. When
the monitor receives a break signal, it drives the PTA0 pin high for the
duration of two bits and then echoes back the break signal.
Figure 9-6. Break Transaction
9.4.5 Baud Rate
The communication baud rate is controlled by the external frequency
and the divide ratio is 1024.
Table 9-3 has the external frequency required to achieve a standard
baud rate of 9600 bps. Other standard baud rates can be accomplished
using proportionally higher or lower frequency generators. If a crystal is
used as the source, be aware of the upper frequency limit that the MCU
can operate.
BIT 5
START
BIT
BIT 1
NEXT
STOP
BIT
START
BITBIT 2 BIT 3 BIT 4 BIT 7BIT 0
BIT 6
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
MISSING STOP BIT
2-STOP BIT DELAY BEFORE ZERO ECHO
Table 9-3. Monitor Baud Rate Selection
External Frequency IRQ Internal Frequency Baud Rate (bps)
9.8304 MHz
V
TST
or V
DD
2.4576 MHz 9600
—
V
SS
3.2 MHz (Trimmed) 9600