Datasheet

76
AT89C51ID2
4289C–8051–11/05
Keyboard Interface The AT89C51ID2 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 P1 and allow to
exit from idle and power down modes.
The keyboard interface interfaces with the C51 core through 3 special function registers:
KBLS, the Keyboard Level Selection register (Table 61), KBE, The Keyboard interrupt
Enable register (Table 60), and KBF, the Keyboard Flag register (Table 59).
Interrupt 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 27). As detailed in Figure 28 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 27. Keyboard Interface Block Diagram
Figure 28. Keyboard Input Circuitry
Power Reduction Mode P1 inputs allow exit from idle and power down modes as detailed in Section “Power
Management”, page 72.
P1:x
KBE. x
KBF. x
KBLS. x
0
1
Vcc
Internal Pullup
P1.0
Keyboard Interface
Interrupt Request
KBD
IE1
Input Circuitry
P1.1 Input Circuitry
P1.2 Input Circuitry
P1.3 Input Circuitry
P1.4 Input Circuitry
P1.5 Input Circuitry
P1.6 Input Circuitry
P1.7 Input Circuitry
KBDIT