at89c5131 ATMEL Corporation, at89c5131 Datasheet - Page 85

• Manufacturer Part Number: at89c5131
• Description: 8-bit Flash Microcontroller With Full Speed Usb Device At89c5131
• Manufacturer: ATMEL Corporation

Keyboard Interface
Introduction
Description
Interrupt
84
AT89C5131
The AT89C5131 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 an alternate function of P1 and allow to
exit from idle and power down modes.
The keyboard interface communicates with the C51 core through 3 special function reg-
isters: KBLS, the Keyboard Level Selection register (Table 71), KBE, The Keyboard
interrupt Enable register (Table 70), and KBF, the Keyboard Flag register (Table 69).
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 37). As detailed in Figure 38 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 allow keyboard arrangement from 1 by n to 8 by n matrix and allow usage
of P1 inputs for other purpose.
Figure 37. Keyboard Interface Block Diagram
Figure 38. Keyboard Input Circuitry
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
P1:x
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Vcc
Internal Pull-up
KBLS.x
0
1
KBF.x
KBD
IE1.0
KBE.x
Keyboard Interface
Interrupt Request
KBDIT
4136C–USB–04/05