MOTOROLA
MC68341 USER’S MANUAL
7- 31
7.4.1.10 MODULE CONFIGURATION REGISTER (MCR). The MCR controls the serial
module configuration. This register can be either read or written when the module is
enabled and is in the supervisor state. The MCR is not affected by a CPU32 RESET
instruction. Only the MCR can be accessed when the module is disabled (i.e., the STP bit
in the MCR is set).
MCR
$700
15
14
13
12
11
10
9876543210
STP
FRZ1
FRZ0
ICCS
0
000
SUPV
000
IARB
RESET:
0
000000010000000
Read/Write
Supervisor Only
STP—Stop Mode Bit
1 = The serial module will be disabled. Setting the STP bit stops all clocks within the
serial module (including the crystal or external clock and SCLK), except for the
clock from the IMB. The clock from the IMB remains active to allow CPU32
access to the MCR. The clock stops on the low phase of the clock and remains
stopped until the STP bit is cleared by the CPU32 or a hardware reset. Accesses
to serial module registers while in stop mode produce a bus error. The serial
module should be disabled in a known state prior to setting the STP bit;
otherwise, unpredictable results may occur. The STP bit should be set prior to
executing the LPSTOP instruction to reduce overall power consumption.
0 = The serial module is enabled and will operate in normal mode. When STP = 0,
make sure the external crystal is stable (XTAL_RDY bit (bit 3) of the ISR is zero)
before continuing.
NOTE
The serial module should be disabled (i.e., the STP bit in the
MCR is set) before executing the LPSTOP instruction to obtain
the lowest power consumption. The X1/X2 oscillator will
continue to run during LPSTOP if STP = 0.
FRZ1–FRZ0—Freeze
These bits determine the action taken when the FREEZE signal is asserted on the IMB
when the CPU32 has entered background debug mode. Table 7-6 lists the action taken
for each combination of bits.
Table 7-6. FRZx Control Bits
FRZ1
FRZ0
Action
0
Ignore FREEZE
0
1
Reserved (FREEZE Ignored)
1
0
Freeze on Character Boundary
1
Freeze on Character Boundary
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
..
.