![](http://datasheet.mmic.net.cn/290000/XPC801ZP25_datasheet_16187868/XPC801ZP25_450.png)
Development Support
MOTOROLA
MPC801 USER’S MANUAL
18-39
18
The sequencing error encoding indicates that the external development tool inputs are not
what the development port and/or the core was expecting. There are two possible causes
of this error:
The processor was trying to read instructions and data was shifted into the
development port.
The processor was trying to read data and an instruction was shifted into the
development port.
Nonetheless, the port terminates the read cycle with a bus error. In turn, this bus error
causes the core to signal that an interrupt exception has occurred. Since a status of
sequencing error has higher priority than an exception, the port reports the sequencing error
first and the core interrupt on the next transmission. The development port ignores the
command, instruction, or data shifted in while the sequencing error or core interrupt is
shifted out. The next transmission, after all error status is reported to the port, should either
be a new instruction, trap enable, or command.
When an interrupt encoding occurs, it indicates that the core has encountered an interrupt
while executing the previous instruction in debug mode. Interrupts can occur as a result of
instruction execution either because of memory access faults or from unmasked external
interrupts. When an interrupt occurs, the development port ignores the command,
instruction, or data shifted in while the interrupt encoding was shifting out. The next
transmission to the port should be a new instruction, trap enable, or debug port command.
Finally, the null encoding indicates that no data has been transferred from the core to the
development port shift register.
A fast download procedure is used to download a block of data from the debug tool into the
system memory. This procedure can be accomplished by repeating the following sequence
of transactions from the development tool to the debug port for the number of data words to
be downloaded.
INIT:Save RX, RY
RY <- Memory Block address- 4
repeat:mfsprRX, DPDR
DATA word to be moved to memory
stwuRX, 0x4(RY)
until here
Restore RX,RY
Figure 18-12. Example of Download Procedure Code