MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-46
4.6.4.2 LPSTOP Broadcast Cycle
Low power stop mode is initiated by the CPU32. Individual modules can be stopped
by setting the STOP bits in each module configuration register. The SCIM2E can turn
off system clocks after execution of the LPSTOP instruction. When the CPU32 exe-
cutes LPSTOP, a low power stop broadcast cycle is generated. The SCIM2E brings
the MCU out of low power mode when either a reset or an interrupt of higher priority
than the interrupt mask level in the CPU32 condition code register occurs.
UNIT for more information.
During an LPSTOP broadcast cycle, the CPU32 performs a CPU space write to
address 0x3FFFE. This write puts a copy of the interrupt mask value in the clock con-
trol logic. The mask is encoded on the data bus as shown in Figure 4-15.
The LPSTOP CPU space cycle is shown externally (if the bus is available) as an indi-
cation to external devices that the MCU is going into low power stop mode. The
SCIM2E provides an internally generated DSACK response to this cycle. The timing
of this bus cycle is the same as for a fast termination write cycle. If the bus is not avail-
able (arbitrated away), the LPSTOP broadcast cycle is not shown externally.
NOTE
BERR assertion during the LPSTOP broadcast cycle is ignored.
Figure 4-15 LPSTOP Interrupt Mask Encoding on DATA[15:0]
4.6.5 Bus Exception Control Cycles
An external device or a chip-select circuit must assert at least one of the DSACK[1:0]
signals or the AVEC signal to terminate a bus cycle normally. Bus exception control
cycles are used when bus cycles are not terminated in the expected manner.
Acceptable bus cycle termination sequences are summarized as follows. The case
numbers refer to Table 4-21, which indicates the results of each type of bus cycle
termination.
Normal Termination
— DSACK is asserted; BERR and HALT remain negated (case 1).
Halt Termination
— HALT is asserted at the same time or before DSACK, and BERR remains
negated (case 2).
Bus Error Termination
— BERR is asserted in lieu of, at the same time as, or before DSACK (case 3),
LPSTOP MASK LEVEL
15
8
7
0
IP MASK
14 13 12 11 10
9
6
5
4
3
2
1
000
0000000000
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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