
MPC562/MPC564 Compression Features
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
A-15
A.3.1.1
Decompression Off Mode
A.3.1.2
Decompression On Mode
In this mode, the MPC562/MPC564’s RCPU sends the two-bit aligned change of flow (COF) address to
the BBC. The BIU transfers the word portion of the address to the U-bus. The BBC continues to pre-fetch
the data from the consequent memory addresses regardless of whether the RCPU requests them in order
to supply data to the ICDU.
In the MPC562/MPC564, the data coming from the instruction memory is not provided directly to the
RCPU, but loaded into the ICDU for decompression. Decompressed instruction code together with “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
In this mode the MPC562/MPC564’s ICDU DECRAM is used as a decompressor vocabulary storage and
may not be used as a general purpose RAM.
A.3.1.2.1
Show Cycles in Decompression On Mode
In the MPC562/MPC564’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 MPC562/MPC564 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)