mc68hc908gr8b Freescale Semiconductor, Inc, mc68hc908gr8b Datasheet - Page 224

• Manufacturer Part Number: mc68hc908gr8b
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Development Support
18.3.1.4 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.
18.3.1.5 Break Signal
A start bit (0) followed by nine 0 bits is a break signal. When the monitor receives a break signal, it drives
the PTA0 pin high for the duration of approximately two bits and then echoes back the break signal.
18.3.1.6 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 18-1
effective baud rate is the bus frequency divided by 256. If using a crystal as the clock source, be aware
of the upper frequency limit that the internal clock module can handle. See
Characteristics
18.3.1.7 Commands
The monitor ROM firmware uses these commands:
The monitor ROM firmware echoes each received byte back to the PTA0 pin for error checking. An 11-bit
delay at the end of each command allows the host to send a break character to cancel the command. A
delay of two bit times occurs before each echo and before READ, IREAD, or READSP data is returned.
The data returned by a read command appears after the echo of the last byte of the command.
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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 9600 bps. The
Wait one bit time after each echo before sending the next byte.
or
START
19.6 3.0 V DC Electrical Characteristics
BIT
0
BIT 0
1
2
BIT 1
TST
MISSING STOP BIT
3
Figure 18-12. Monitor Data Format
) upon entry into monitor mode. If monitor mode was entered with V
Figure 18-13. Break Transaction
4
MC68HC908GR8B Data Sheet, Rev. 3.0
BIT 2
5
6
BIT 3
7
BIT 4
NOTE
BIT 5
APPROXIMATELY 2 BITS DELAY
BEFORE ZERO ECHO
for this limit.
BIT 6
0
1
BIT 7
2
3
STOP
BIT
4
19.5 5.0 V DC Electrical
START
NEXT
5
BIT
6
Freescale Semiconductor
7
DD