Microcontrollers Data Sheet

Development Support
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
260 Freescale Semiconductor
18.3.1.5 Echoing
As shown in Figure 18-11, the monitor ROM immediately echoes each received byte back to the PTA0
pin for error checking.
Figure 18-11. Read Transaction
Any result of a command appears after the echo of the last byte of the command.
18.3.1.6 Break Signal
A start bit followed by nine low bits is a break signal. See Figure 18-12. When the monitor receives a break
signal, it drives the PTA0 pin high for the duration of two bits before echoing the break signal.
Figure 18-12. Break Transaction
18.3.1.7 Commands
The monitor ROM uses these commands (see Table 18-3–Table 18-8):
• READ, read memory
• WRITE, write memory
• IREAD, indexed read
• IWRITE, indexed write
• READSP, read stack pointer
• RUN, run user program
ADDR. HIGHREADREAD ADDR. HIGH ADDR. LOW ADDR. LOW DATA
ECHO
SENT TO
MONITOR
RESULT
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