MC68HC908GZ8 FREESCALE [Freescale Semiconductor, Inc], MC68HC908GZ8 Datasheet - Page 281

• Manufacturer Part Number: MC68HC908GZ8
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

20.3.1.4 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.
20.3.1.5 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.
20.3.1.6 Baud Rate
The communication baud rate is controlled by the crystal frequency or external clock and the state of the
PTB4 pin (when IRQ is set to V
on IRQ and the reset vector blank, then the baud rate is independent of PTB4.
Table 20-1
effective baud rate is the bus frequency divided by 278. If using a crystal as the clock source, be aware
of the upper frequency limit that the internal clock module can handle. See
or
20.3.1.7 Commands
The monitor ROM firmware uses these commands:
Freescale Semiconductor
21.6 3.3-Vdc Electrical Characteristics
•
•
•
•
•
•
READ (read memory)
WRITE (write memory)
IREAD (indexed read)
IWRITE (indexed write)
READSP (read stack pointer)
RUN (run user program)
also lists external frequencies required to achieve a standard baud rate of 7200 bps. The
User
Monitor
Modes
START
BIT
Vector High
0
$FFFE
$FEFE
Reset
BIT 0
1
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
2
BIT 1
TST
MISSING STOP BIT
3
Vector Low
Figure 20-11. Monitor Data Format
) upon entry into monitor mode. If monitor mode was entered with V
$FFFF
$FEFF
Figure 20-12. Break Transaction
4
Reset
BIT 2
Table 20-2. Mode Differences
5
6
for this limit.
BIT 3
Vector High
7
$FFFC
$FEFC
Break
BIT 4
Functions
BIT 5
Vector Low
APPROXIMATELY 2 BITS DELAY
BEFORE ZERO ECHO
$FEFD
$FFFD
Break
BIT 6
0
1
BIT 7
2
Vector High
$FFFC
$FEFC
3
STOP
SWI
BIT
4
21.7 5.0-Volt Control Timing
START
NEXT
5
BIT
6
Vector Low
$FEFD
$FFFD
SWI
7
Monitor ROM (MON)
DD
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