MC68332ACEH20 Datasheet, PDF (29/88 Pages) Freescale Semiconductor, Inc – 32-Bit Modular Microcontroller

Freescale Semiconductor, Inc.
ADDR0 also affects the operation of the data multiplexer. During an operand transfer, ADDR[23:1] in-
dicate the word base address of the portion of the operand to be accessed, and ADDR0 indicates the
byte offset from the base.
3.4.11 Misaligned Operands
CPU32 processor architecture uses a basic operand size of 16 bits. An operand is misaligned when it
overlaps a word boundary. This is determined by the value of ADDR0. When ADDR0 = 0 (an even ad-
dress), the address is on a word and byte boundary. When ADDR0 = 1 (an odd address), the address
is on a byte boundary only. A byte operand is aligned at any address; a word or long-word operand is
misaligned at an odd address. The CPU32 does not support misaligned operand transfers.
The largest amount of data that can be transferred by a single bus cycle is an aligned word. If the MCU
transfers a long-word operand via a 16-bit port, the most significant operand word is transferred on the
first bus cycle and the least significant operand word on a following bus cycle.
3.4.12 Operand Transfer Cases
The following table summarizes how operands are aligned for various types of transfers. OPn entries
are portions of a requested operand that are read or written during a bus cycle and are defined by SIZ1,
SIZ0, and ADDR0 for that bus cycle.
Table 11 Operand Alignment
Transfer Case
Byte to 8-Bit Port (Even/Odd)
Byte to 16-Bit Port (Even)
Byte to 16-Bit Port (Odd)
Word to 8-Bit Port (Aligned)
Word to 8-Bit Port (Misaligned)³
Word to 16-Bit Port (Aligned)
Word to 16-Bit Port (Misaligned)³
3 Byte to 8-Bit Port (Aligned)²
3 Byte to 8-Bit Port (Misaligned)^{2, 3}
3 Byte to 16-Bit Port (Aligned)²
3 Byte to 16-Bit Port (Misaligned)^{2, 3}
Long Word to 8-Bit Port (Aligned)
Long Word to 8-Bit Port (Misaligned)³
Long Word to 16-Bit Port (Aligned)
Long Word to 16-Bit Port (Misaligned)³
SIZ1
0
0
0
1
1
1
1
1
1
1
1
0
1
0
1
SIZ0
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
ADDR0
X
0
1
0
1
0
1
0
1
0
1
0
1
0
1
DSACK1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
DSACK0
0
X
X
0
0
X
X
0
0
X
X
0
0
X
X
DATA
[15:8]
OP0
OP0
(OP0)
OP0
OP0
OP0
(OP0)
OP0
OP0
OP0
(OP0)
OP0
OP0
OP0
(OP0)
DATA
[7:0]
(OP0)
(OP0)
OP0
(OP1)
(OP0)
OP1
OP0
(OP1)
(OP0)
OP1
OP0
(OP1)
(OP0)
OP1
OP0
NOTES:
1. Operands in parentheses are ignored by the CPU32 during read cycles.
2. Three-byte transfer cases occur only as a result of a long word to byte transfer.
3. The CPU32 does not support misaligned word or long-word transfers.
3.5 Chip Selects
Typical microcontrollers require additional hardware to provide external chip-select signals. Twelve in-
dependently programmable chip selects provide fast two-cycle access to external memory or peripher-
als. Address block sizes of 2 Kbytes to 1 Mbyte can be selected.
MC68332
MC68332TS/D
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