4- 20
MC68349 USER'S MANUAL
MOTOROLA
The number of wait states programmed into the internal wait state generation logic by a
chip select can be used even though the pin is not used as a CS≈ signal. The programmed
number of wait states in the CS≈ signal applies to the port B pins configured as IRQ≈ or
I/O pins. This is done by programming the chip select with the number of wait states to be
added, as though it were to be used. The EDS bit in the base address register along with
the DD1/DD0 and PS1/PS0 bits in the chip select address mask register must be set to
add the desired number of wait states (the V-bit in the module base address register must
also be set).
4.2.6 Low-Power Stop
Executing the LPSTOP instruction provides reduced power consumption when the
MC68349 is idle; only the SIM49 remains active. Operation of the SIM49 clock and
CLKOUT during LPSTOP is controlled by the STSIM and STEXT bits in the SYNCR (see
Table 4-3). LPSTOP disables the clock to the software watchdog in the low state. The
software watchdog remains stopped until the LPSTOP mode ends; it begins to run again
on the next rising clock edge.
NOTE
When the CPU32+ executes the STOP instruction (as opposed
to LPSTOP), the software watchdog continues to run. If the
software watchdog is enabled, it issues a reset or interrupt
when timeout occurs.
The periodic interrupt timer does not respond to an LPSTOP instruction; thus, it can be
used to exit LPSTOP as long as the interrupt request level is higher than the CPU32+
interrupt mask level. To stop the periodic interrupt timer while in LPSTOP, the PITR must
be loaded with a zero value before LPSTOP is executed. The bus monitor, double bus
fault monitor, and spurious interrupt monitor are all inactive during LPSTOP.
The STP bit in the MCR of each on-chip module (DMA, quad data memory, and serial
modules) should be set prior to executing the LPSTOP instruction. Setting the STP bit
stops all clocks within each of the modules, except for the clock from the IMB. The clock
from the IMB remains active to allow the CPU32+ access to the MCR of each module. The
system clock stops on the low phase of the clock and remains stopped until the STP bit is
cleared by the CPU32+ or until reset. For more information, see the description of the
MCR STP bit for each module.
If an external device requires additional time to prepare for entry into LPSTOP mode, entry
can be delayed by asserting HALT (see Section 3 Bus Operation ).