MC9S08RC8 Datasheet, PDF (125/234 Pages) Freescale Semiconductor, Inc – Microcontrollers

Keyboard Interrupt (KBI) Block Description
9.2 KBI Block Diagram
Figure 9-2 shows the block diagram for a KBI module.
KBIxP0
KBIPE0
KBIxP3
KBIxP4
KBIPE3
1
0 _{S KBIPE4}
KBEDG4
KBIxPn
1
0 _{S KBIPEn}
V_DD
D ^CLR Q
CK
KBACK
RESET
BUSCLK
KBF
SYNCHRONIZER
KBIMOD
KEYBOARD
INTERRUPT FF
STOP ^{STOP BYPASS}
KBIE
KEYBOARD
INTERRUPT
REQUEST
KBEDGn
Figure 9-2. KBI Block Diagram
The KBI module allows up to eight pins to act as additional interrupt sources. Four of these pins allow
falling-edge sensing while the other four can be configured for either rising-edge sensing or falling-edge
sensing. The sensing mode for all eight pins can also be modified to detect edges and levels instead of only
edges.
9.3 Keyboard Interrupt (KBI) Module
This on-chip peripheral module is called a keyboard interrupt (KBI) module because originally it was
designed to simplify the connection and use of row-column matrices of keyboard switches. However, these
inputs are also useful as extra external interrupt inputs and as an external means of waking up the MCU
from stop or wait low-power modes.
9.3.1 Pin Enables
The KBIPEn control bits in the KBIxPE register allow a user to enable (KBIPEn = 1) any combination of
KBI-related port pins to be connected to the KBI module. Pins corresponding to 0s in KBIxPE are
general-purpose I/O pins that are not associated with the KBI module.
9.3.2 Edge and Level Sensitivity
Synchronous logic is used to detect edges. Prior to detecting an edge, enabled keyboard inputs in a KBI
module must be at the deasserted logic level.
A falling edge is detected when an enabled keyboard input signal is seen as a logic 1 (the deasserted level)
during one bus cycle and then a logic 0 (the asserted level) during the next cycle.
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
Freescale Semiconductor
125