AN662 Ver la hoja de datos (PDF) - Microchip Technology
Número de pieza
componentes Descripción
Fabricante
AN662 Datasheet PDF : 17 Pages
| |||
FIGURE 4: HCS300 BLOCK DIAGRAM
Oscillator
Reset circuit
Controller
Power
latching
and
switching
LED
LED driver
PWM
EEPROM
Encoder
32-bit shift register
VSS
VDD
Button input port
S3 S2 S1 S0
AN665
The IBM PC-AT® Keyboard Protocol
IBM® was the first to introduce the synchronous serial
protocol most of today’s PC-ATs use to communicate
with a keyboard. This now-standard, 5-pole shielding
connector (Figure 5) carries the clock line, data line,
ground, and +5V power supply in order to transmit data
bidirectionally from the keyboard to the PC.
Typically, data travelling from the keyboard to the PC is
accomplished by either key pressure or release infor-
mation. However, some configuration data (i.e., repeat,
delay, and rate) can flow in the opposite direction – for
example, during a system boot. The keyboard drives
the clock line by using open collector drivers. To disable
the keyboard, the PC can keep the clock line low. If the
data line is held low by the PC while the clock line is
high, the computer transmits a requests to send, and
the keyboard goes into receive mode. The keyboard is
only allowed to send data when both the clock line and
data line are high.
FIGURE 5: STANDARD 5-POLE CONNECTOR
1
3
42 5
1 = Clock
2 = Data
3 = GND
4 = GND
5 = +5V
FIGURE 6: AT® KEYBOARD PROTOCOL
Keyboard
Clock
Keyboard
Data
PC
Data
1 2 3 4 5 6 7 8 9 10 11
Start
Bit
LSB
LSB
Start
Bit
MSB
Parity
Stop
Bit
MSB
Parity
Stop
Bit
Keyboard pulls low
ã 1997 Microchip Technology Inc.
DS00665A-page 3
Share Link: 