
MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-38
to what states DSACK[1:0] must be driven — either by a chip select or by external cir-
cuitry — to terminate the given bus cycle.
4.6 Bus Operation
Internal microcontroller modules are typically accessed in two system clock cycles.
Regular external bus cycles use handshaking between the MCU and external periph-
erals to manage transfer size and data. These accesses take a minimum of three
system clock cycles, with no wait states. During regular cycles, wait states can be
information.
Fast-termination cycles, which are two clock external accesses with no wait states,
use chip-select logic to generate handshaking signals internally. Refer to 4.6.3 Fast information about each type of bus cycle.
Table 4-20 Operand Alignment
Current
Cycle
Transfer Case
SIZ1
SIZ0
ADDR0
DSACK1 DSACK0
DATA
[15:8]
DATA
[7:0]
Next
Cycle
1
Byte to 8-bit port (even)
0
1
0
1
0
OP0
(OP0)1
NOTES:
1. Operands in parentheses are ignored by the CPU32 during read cycles.
—
2
Byte to 8-bit port (odd)
0
1
0
OP0
(OP0)
—
3
Byte to 16-bit port (even)
0
1
0
1
OP0
(OP0)
—
4
Byte to 16-bit port (odd)
0
1
0
1
(OP0)
OP0
—
5
Word to 8-bit port
(aligned)
1
0
1
0
OP0
(OP1)
2
6
Word to 8-bit port
(misaligned
1
0
1
0
OP0
(OP0)
1
7
Word to 16-bit port
(aligned)
10
0
1
OP0
OP1
—
8
Word to 16-bit port
(misaligned)
10
1
0
1
(OP0)
OP0
3
9
Long-word to 8-bit port
(aligned)
0
1
0
OP0
(OP1)
13
10
Long-word to 8-bit port
(misaligned)2
2. The CPU32 does not support misaligned operand transfers.
1
0
1
0
OP0
(OP0)
1
11
Long-word to 16-bit port
(aligned)
00
0
1
OP0
OP1
7
12
Long-word to 16-bit port
(misaligned)2
10
1
0
1
(OP0)
OP0
3
13
Three byte to 8-bit port3
3. Three byte transfer cases occur only as a result of an aligned long word to 8-bit port transfer.
1
0
OP0
(OP0)
5
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