2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
1
DEVICES AND COMMUNICATION
BUSES FOR DEVICES NETWORK–
Lesson-6: Parallel port at devices
2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
2
Parallel Port
λ 8-bit IOs
λ Short distances, generally within a
circuit board or IC or nearby external
devices
2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
3
Parallel port in the devices
• Advantage− Number of 8 bits over the
wires in parallel.
• High data transfer rate
• Disadvantage− More number of wires
• Capacitive effect in parallel wires reduces
the length up to which communication in
parallel can take place.
• High capacitance results in delay for the
bits at the other end undergoing transition
from 0 to 1 or 1 to 0.
2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
4
Parallel port in the devices
• Disadvantage− High capacitance can
also result in noise and cross talk
(induced signals) between the wires.
2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
5
Port Interfacing
λ IO device interfacing-circuit with the
processor and system buses and connections
to external peripherals/systems
λ Parallel port inputs I0 to I7 may be from a
keypad controller.
λ Parallel port outputs O0 to O7 may be
output bits to LCD display output
controller.
λ Bri and Bro buffers may be provided at bi-
directional I/O port
2008
Chapter-3 L06: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
6
Parallel port interfacings for keypad, LCD display and modem
CS-Port Select
BRi-Buffer Register
for Input
BRo-Buffer Register
for Output
An Input Port
An Output Port
An I/O Port
CS
IORD