HCS08 datasheet(152/290 Pages) MOTOROLA

152 / 290 page

Keyboard Interrupt (KBI) Module

MC9S08GB/GT

152

MOTOROLA

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.

A rising edge is detected when the input signal is seen as a logic 0 during one bus cycle and then a logic 1

during the next cycle.

The KBIMOD control bit can be set to reconfigure the detection logic so that it detects edges and levels.

In KBIMOD = 1 mode, the KBF status flag becomes set when an edge is detected (when one or more

enabled pins change from the deasserted to the asserted level while all other enabled pins remain at their

deasserted levels), but the flag is continuously set (and cannot be cleared) as long as any enabled keyboard

input pin remains at the asserted level. When the MCU enters stop mode, the synchronous edge-detection

logic is bypassed (because clocks are stopped). In stop mode, KBI inputs act as asynchronous

level-sensitive inputs so they can wake the MCU from stop mode.

9.4.3 KBI Interrupt Controls

The KBF status flag becomes set (1) when an edge event has been detected on any KBI input pin. If

KBIE = 1 in the KBISC register, a hardware interrupt will be requested whenever KBF = 1. The KBF flag

is cleared by writing a 1 to the keyboard acknowledge (KBACK) bit.

When KBIMOD = 0 (selecting edge-only operation), KBF is always cleared by writing 1 to KBACK.

When KBIMOD = 1 (selecting edge-and-level operation), KBF cannot be cleared as long as any keyboard

input is at its asserted level.

9.5 KBI Registers and Control Bits

This section provides information about all registers and control bits associated with the KBI modules.

Refer to the direct-page register summary in the Memory section of this data sheet for the absolute address

assignments for all KBI registers. This section refers to registers and control bits only by their names. A

Motorola-provided equate or header file is used to translate these names into the appropriate absolute

addresses.

9.5.1 KBI Status and Control Register (KBISC)

Figure 9-4 KBI Status and Control Register (KBISC)

Bit 7

654321

Bit 0

Read:

KBEDG7

KBEDG6

KBEDG5

KBEDG4

KBF

KBIE

KBIMOD

Write:

KBACK

Reset:

00000000

= Unimplemented or Reserved

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