AT89C51RD2 Atmel Corporation, AT89C51RD2 Datasheet - Page 59

• Manufacturer Part Number: AT89C51RD2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RD2

• Flash (kbytes): 64 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 2
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART
• Watchdog: Yes

15. Keyboard Interface
15.0.1
15.0.2
4235K–8051–05/08
Interrupt
Power Reduction Mode
The AT89C51RD2/ED2 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 interfaces with the C51 core through 3 special function registers: KBLS, the Key-
board Level Selection register (Table 15-3), KBE, the Keyboard interrupt Enable register
(Table 15-2), and KBF, the Keyboard Flag register (Table 15-1).
The keyboard inputs are considered as 8 independent interrupt sources sharing the same inter-
rupt vector. An interrupt enable bit (KBD in IE1) allows global enable or disable of the keyboard
interrupt (see Figure 15-1). As detailed in Figure 15-2 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 allows usage of P1
inputs for other purpose.
Figure 15-1. Keyboard Interface Block Diagram
Figure 15-2. Keyboard Input Circuitry
P1 inputs allow exit from idle and power-down modes as detailed in Section “Power Manage-
ment”, page 80.
P1:x
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
AT89C51RD2/ED2
KBD
IE1
Keyboard Interface
Interrupt Request
KBDIT
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