MC908KX2MDWE Datasheet, PDF (177/210 Pages) Freescale Semiconductor, Inc – High-performance M68HC08 architecture, Fully upward-compatible object code with M6805, M146805, and M68HC05 Families

Monitor ROM (MON)
16.3.1.5 Data Format
The MCU waits for the host to send eight security bytes (see 16.3.2 Security). After the security bytes, the
MCU sends a break signal (10 consecutive 0s) to the host computer, indicating that it is ready to receive
a command.
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.
START
BIT BIT 0
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5
NEXT
START
BIT 6 BIT 7 STOP BIT
BIT
Figure 16-10. Monitor Data Format
16.3.1.6 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 two bits and then echoes back the break signal.
MISSING STOP BIT
2-STOP BIT DELAY BEFORE ZERO ECHO
01234567
01234567
Figure 16-11. Break Transaction
16.3.1.7 Baud Rate
The communication baud rate is controlled by the CGMXCLK frequency output of the internal clock
generator module.
16.3.1.8 Force Monitor Mode
In forced monitor mode, the baud rate is fixed at CGMXCLK/1024. A CMGXCLK frequency of 4.9152 MHz
results in a 4800 baud rate. A 9.8304-MHz frequency produces a 9600 baud rate.
16.3.1.9 Normal Monitor Mode
In normal monitor mode, the communication baud rate is controlled by the CGMXCLK frequency output
of the internal clock generator module. Table 16-3 lists CGMXCLK frequencies required to achieve
standard baud rates. Other standard baud rates can be accomplished using other clock frequencies. The
internal clock can be used as the clock source by programming the internal clock generator registers
however, monitor mode will always be entered using the external clock as the clock source.
Table 16-3. Normal Monitor Mode Baud Rate Selection
CGMXCLK Frequency (MHz)
9.8304
Baud Rate
9600
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor
177