Datasheet

Functional Description
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor 121
8.3.5 Commands
The monitor ROM firmware uses these commands:
• READ (read memory)
• WRITE (write memory)
• IREAD (indexed read)
• IWRITE (indexed write)
• READSP (read stack pointer)
• RUN (run user program)
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.
NOTE
Wait one bit time after each echo before sending the next byte.
Figure 8-5. Read Transaction
Figure 8-6. Write Transaction
A brief description of each monitor mode command is given in Table 8-4 through Table 8-9.
READ
READ
ECHO
FROM HOST
ADDRESS
HIGH
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
RETURN
1 3, 2114
4
Notes:
2 = Data return delay, 2 bit times
3 = Cancel command delay, 11 bit times
4 = Wait 1 bit time before sending next byte.
44
1 = Echo delay, 2 bit times
WRITE
WRITE
ECHO
FROM HOST
ADDRESS
HIGH
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
DATA
Notes:
2 = Cancel command delay, 11 bit times
3 = Wait 1 bit time before sending next byte.
11311
3
3
3 2, 3
1 = Echo delay, 2 bit times