Functional Description
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.
FROM HOST
ADDRESS
HIGH
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
READ
READ
DATA
4
4
1
1
4
1
3, 2
4
ECHO
RETURN
Notes:
1 = Echo delay, 2 bit times
2 = Data return delay, 2 bit times
3 = Cancel command delay, 11 bit times
4 = Wait 1 bit time before sending next byte.
Figure 8-5. Read Transaction
FROM HOST
ADDRESS
HIGH
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
DATA
WRITE
1
WRITE
3
3
1
3
1
3
1
2, 3
ECHO
Notes:
1 = Echo delay, 2 bit times
2 = Cancel command delay, 11 bit times
3 = Wait 1 bit time before sending next byte.
Figure 8-6. Write Transaction
A brief description of each monitor mode command is given in Table 8-4 through Table 8-9.
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor
121
FREESCALE [ Freescale ]
