System Integration Block (SIB)
3-64
MC68302 USER’S MANUAL
MOTOROLA
LPP16—Low-power Clock Prescale Divide by 16
0 = The low-power clock divider input clock is the main clock.
1 = The low-power clock divider input clock is the main clock divided by 16. Thus,
a divide ratio of 32 to 1024 (LPCD4—LPCD0 0 to 31) can be selected.
After a system reset, this bit defaults to zero.
LPREC—Low-Power Recovery
0 = Nondestructive recovery from low power. The processor returns to full frequency
and then proceeds using currently held status value. This is called low-power
mode.
1 = Destructive recovery from low power. The processor returns to full frequency and
then drives RESET for 16 clock cycles. This is called lowest power mode.
After a system reset, the bit defaults to zero.
3.9 CLOCK CONTROL REGISTER
The CKCR is a 16-bit register is a memory-mapped read-write register. The address of this
register is fixed at $0FA in supervisor data space (FC = 5). This register controls the state
of CLKO, RCLK1, TCLK1, and BRG1. This register is cleared at reset.
CLKOM—CLKO Mode
These bits may be written at any time to change the mode of the CLKO pin. Changes to
CLKO are made while the CLKO signal is high. No spikes on CLKO will occur when the
CLKOM bits are changed.
00 = The CLKO pin functions normally
01 = The CLKO pin output driver is two thirds its normal strength. Specification 5a at
16.67 MHz is 2 to 14 ns and at 20 MHz is 2 to 11 ns. The output drive derating
factor for CLKO in this mode is not specified.
01 = The CLKO pin output driver is one third its normal strength. Specification 5a at
16.67 MHz is 2 to 20ns and at 20 MHz is 2 to 16ns. The output drive derating fac-
tor for CLKO in this mode is not specified.
11 = The CLKO pin output is disabled, but is driven high by an internal pullup. Signifi-
cant power savings can be obtained by disabling CLKO. Typical power savings
may range between 2 and 6 mA, depending on the CLKO loading. Disabling
CLKO can also reduce noise and electromagnetic interference on the printed cir-
cuit board.
TSTCLK1—Three-state TCLK1
0 = Normal operation
1 = The TCLK1 pin is three-stated. This option may be used to prevent contention on
the TCLK1 pin if an external clock is provided to the TCLK1 pin while the SCC1
baud rate generator is output on TCLK1. This option may also be chosen if it is re-
quired to run the SCC1 baud rate generator at high speed (for instance in a high
speed UART application), but the TCLK1 output is not needed, and it is desired to
15
CLKOM
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
TSTCLK1 TSRCLK1 DBRG1
RESERVED