at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 128

• Manufacturer Part Number: at89c51re2-slsem
• Description: At89c51re2 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

Keyboard Interface
Interrupt
Power Reduction Mode
7663B–8051–03/07
P1:x
The AT89C51RE2 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 91), KBE, The Keyboard interrupt
Enable register (Table 90), and KBF, the Keyboard Flag register (Table 89).
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 31). As detailed in Figure 32 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 31. Keyboard Interface Block Diagram
Figure 32. Keyboard Input Circuitry
P1 inputs allow exit from idle and power down modes as detailed in Section “Power
Management”, page 102.
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
Vcc
Internal Pullup
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
Input Circuitry
KBLS. x
0
1
KBF. x
KBE. x
KBD
IE1
Keyboard Interface
Interrupt Request
KBDIT
111