Motorola MPC533 Reference Manual page 914

Development Port
at the same time. Since it is not possible for a sequencing error to occur and also have valid
data there is no priority conflict with the sequencing error status. Also, any interrupt that is
recognized at the same time that there is valid data is not related to the execution of an
instruction. Therefore, a valid data status will be output and the interrupt status will be
saved for the next transmission.
The sequencing error encoding indicates that the inputs from the external development tool
are not what the development port and/or the CPU was expecting. Two cases could cause
this error:
1. The processor was trying to read instructions and there was data shifted into the
development port, or
2. The processor was trying to read data and there was instruction shifted into the
development port. The port will terminate the read cycle with a bus error.
This bus error will cause the CPU to signal that an interrupt (exception) occurred. Since a
status of sequencing error has a higher priority than exception, the port will report the
sequencing error first, and the CPU interrupt on the next transmission. The development
port will ignore the command, instruction, or data shifted in while the sequencing error or
CPU interrupt is shifted out. The next transmission after all error status is reported to the
port should be a new instruction, trap enable or command (possibly the one that was in
progress when the sequencing error occurred).
The interrupt-occurred encoding is used to indicate that the CPU encountered an interrupt
during the execution of the previous instruction in debug mode. Interrupts may 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 port will ignore 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 is used to indicate that no data has been transferred from the CPU
to the development port shift register.
21.4.6.11 Fast Download Procedure
The download procedure is used to download a block of data from the debug tool into
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 down loaded:
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PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
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