Motorola MPC533 Reference Manual page 1050

Operation Modes
"next instruction address" are provided to the RCPU whenever it requires another
instruction fetch.
All addresses issued by the BIU to the U-bus are transferred in parallel to the IMPU. The
IMPU compares the address of the access to its region programming. If any protection
violation is detected by the IMPU, the current U-bus access is aborted by the BIU and an
instruction storage protection error exception is signaled to the RCPU.
Show cycle and program trace access attributes accompanying the COF RCPU access only
are forwarded by the BIU along with the U-bus access. Additional information about the IP
of the compressed instruction address is provided on the U-bus data bus. Refer below to
Section G.3.1.2.1, "Show Cycles in Decompression On Mode," for more details.
In this mode the 's ICDU DECRAM is used as a decompressor vocabulary storage and may
not be used as a general purpose RAM.
G.3.1.2.1 Show Cycles in Decompression On Mode
In the 's decompression on mode, the instruction address consists of an instruction base
address and four bits of the instruction bit pointer. In order to provide the capability to show
full instruction address, including instruction bit pointer on the external bus, show cycle
information is presented not only on the address bus, but also on some bits of the data bus:
• ADDR[0:29] – show the value of the base address of compressed instruction (word
pointer into the memory)
• DATA[0] – shows in which mode the is operating
— 0 = decompression off mode
— 1 = decompression on mode
• DATA[1:4] – represent an instruction bit pointer within the word.
Instruction show cycle bus transactions have the following characteristics (see
Figure 9-41):
• One clock cycle
• Address phase only; in decompression on mode part of the compressed address is
driven on data lines together with address lines. The external bus interface adds one
clock delay between a read cycle and such show cycle.
• STS assertion only (no TA assertion)
The BBCMCR[DECOMP_SC_EN] bit determines if the data
portion (DATA[0:4]) of the instruction show cycle is driven or
not,
(BBCMCR[EN_COMP] bit)
G-18
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
regardless of
MPC533 Reference Manual
decompression mode
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