SYSTEM INTEGRATION MODULE
M68HC16 Z SERIES
5-36
USER’S MANUAL
5.6 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 three system clock cy-
cles, with no wait states. During regular cycles, wait states can be inserted as needed
by bus control logic. Refer to
Fast-termination cycles, which are two-cycle external accesses with no wait states,
use chip-select logic to generate handshaking signals internally. Refer to
and
for more information. Bus control signal
timing, as well as chip-select signal timing, are specified in
. Refer to the
SIM Reference Manual (SIMRM/AD) for more
information about each type of bus cycle.
5.6.1 Synchronization to CLKOUT
External devices connected to the MCU bus can operate at a clock frequency different
from the frequencies of the MCU as long as the external devices satisfy the interface
signal timing constraints. Although bus cycles are classified as asynchronous, they are
interpreted relative to the MCU system clock output (CLKOUT).
Table 5-16 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 CPU16 during read cycles.
—
2
Byte to 8-bit port (odd)
0
1
1
1
0
OP0
(OP0)
—
3
Byte to 16-bit port (even)
0
1
0
0
1
OP0
(OP0)
—
4
Byte to 16-bit port (odd)
0
1
1
0
1
(OP0)
OP0
—
5
Word to 8-bit port
(aligned)
1
0
0
1
0
OP0
(OP1)
2
6
Word to 8-bit port
(misaligned)
1
0
1
1
0
OP0
(OP0)
1
7
Word to 16-bit port
(aligned)
1
0
0
0
1
OP0
OP1
—
8
Word to 16-bit port
(misaligned)
1
0
1
0
1
(OP0)
OP0
3
9
Long word to 8-bit port
(aligned)
0
0
0
1
0
OP0
(OP1)
13
10
Long word to 8-bit port
(misaligned)
2
2. The CPU16 treats misaligned long-word transfers as two misaligned-word transfers.
1
0
1
1
0
OP0
(OP0)
1
11
Long word to 16-bit port
(aligned)
0
0
0
0
1
OP0
OP1
7
12
Long word to 16-bit port
(misaligned)
1
0
1
0
1
(OP0)
OP0
3
13
Three byte to 8-bit port
3
3. Three byte transfer cases occur only as a result of an aligned long word to 8-bit port transfer.
1
1
1
1
0
OP0
(OP0)
5
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..