AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 155

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Keyboard Interface
Introduction
Description
Interrupt
4202D–SCR–06/05
Only for AT8xC5122.
The AT8xC5122/23 implements a keyboard interface allowing the connection of a 8 x n
matrix keyboard. It is based on 8 inputs with programmable interrupt capability on both
high or low level. These inputs are available as alternate function of P5 and allow to exit
from idle and power-down modes.
The keyboard interfaces with the C51 core through 3 special function registers: KBLS,
the Keyboard Level Selection register (Table 96 on page 158), KBE, The Keyboard
interrupt Enable register (Table 95 on page 157), and KBF, the Keyboard Flag register
(Table ).
The keyboard inputs are considered as 8 independent interrupt sources sharing the
same interrupt vector. An interrupt enable bit ( KBD in IE1) allows global enable or dis-
able of the keyboard interrupt (see Figure 98). As detailed in Figure 99 each keyboard
input has the capability to detect a programmable level according to KBLS.x bit value.
Level detection is then reported in interrupt flags KBF.x that can be masked by software
using KBE.x bits.
This structure allows keyboard arrangement from 1 by n to 8 by n matrix and allows
usage of P5 inputs for other purpose.
The KBF.x flags are set by hardware when an active level is on input P5.x. They are
automatically reset after any read access on KBF. If the content of KBF must be ana-
lyzed, the first read instruction must transfer KBF contend to another location. The KBF
register cannot be written by software.
Figure 98. Keyboard Interface Block Diagram
Figure 99. Keyboard Input Circuitry
P5.x
P5.0
P5.1
P5.2
P5.3
P5.4
P5.5
P5.6
P5.7
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
KBLS.x
0
1
KBF.x
KBE.x
IEN1.0
EKB
Keyboard Interface
Interrupt Request
KBDIT
155