Motorola MPC823e Reference Manual page 1100

The sequencing error encoding indicates that the external development tool inputs are not
what the development interface 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 interface port.
• The processor was trying to read data and an instruction was shifted into the
development interface 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 is of higher priority than an exception, the port reports the sequencing error
first and the core interrupt on the next transmission. The development interface port ignores
the command, instruction, or data shifted in while the sequencing error or core interrupt is
shifted out. The next transmission, after the error status is reported to the port, must be
either a new instruction, trap enable, or command.
The interrupt encoding that has occurred indicates that the core encountered an interrupt
while executing the previous instruction in debug mode. Interrupts can occur as the result of
instruction execution (such as unimplemented opcode or arithmetic error), because of a
memory access fault, or from an unmasked external interrupt. When an interrupt occurs, the
development interface port ignores the command, instruction, or data shifted in while the
interrupt encoding was shifting out. The next transmission to the port must 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 interface port shift
register.
The 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:mfspr RX, DPDR
DATA word to be moved to memory
stwu RX, 0x4(RY)
until here
•••
Restore RX,RY
Figure 20-12. Download Procedure Code Example
MOTOROLA
Development Capabilities and Interface
MPC823e REFERENCE MANUAL 20-39