
Low-Power Modes
MC68HC908QL4  MC68HC908QL3  MC68HC908QL2 Data Sheet, Rev. 4
Freescale Semiconductor
93
9.5  Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
9.5.1  Wait Mode
The KBI module remains active in wait mode. Clearing IMASKK in KBSCR enables keyboard interrupt 
requests to bring the MCU out of wait mode.
9.5.2  Stop Mode
The KBI module remains active in stop mode. Clearing IMASKK in KBSCR enables keyboard interrupt 
requests to bring the MCU out of stop mode.
9.6  KBI During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during 
the break state. The BCFE bit in the break flag control register (BFCR) enables software to clear status 
bits during the break state. See BFCR in the SIM section of this data sheet. 
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. If a status bit is cleared 
during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to BCFE. With BCFE cleared (its default state), 
software can read and write registers during the break state without affecting status bits. Some status bits 
have a two-step read/write clearing procedure. If software does the first step on such a bit before the 
break, the bit cannot change during the break state as long as BCFE is cleared. After the break, doing the 
second step clears the status bit.
9.7  I/O Signals
The KBI module can share its pins with the general-purpose I/O pins. See 
Figure 9-1
 for the port pins that 
are shared. 
9.7.1  KBI Input Pins (KBI5:KBI0)
Each KBI pin is independently programmable as an external interrupt source. KBI pin polarity can be 
controlled independently. Each KBI pin when enabled can be configured to use an internal pullup/pulldown 
device using the corresponding PTAPUEx bit see 
12.2.3 Port A Input Pullup/Down Enable Register
. The 
selection of pullup or pulldown is automatically configured to match the polarity selected in KBIPR.
9.8  Registers
The following registers control and monitor operation of the KBI module:
KBSCR (keyboard interrupt status and control register)
KBIER (keyboard interrupt enable register)
KBIPR (keyboard interrupt polarity register)