Digital Logic Fundamentals Unit 9 – Data Bus Control
UNIT 9 – DATA BUS CONTROL
UNIT OBJECTIVE
At the completion of this unit, you will be able to demonstrate computer read and write data
transfer operations by using the DATA BUS CONTROL circuit block.
UNIT FUNDAMENTALS
Via a bidirectional data bus, a computer transfers data between the CPU (central processing
unit) and the memory or input/output devices.
When the CPU is receiving data from a memory or input/output (I/O) device, it is in the read
operating mode. When the CPU is sending data to a memory or I/O device, it is in the write
operating mode.
A R/W (read/write) control signal is output by the CPU to control the direction of data transfer
on the data bus.
When the R/W (designated RD/WR on the circuit board) signal is high, the CPU reads data
from a memory or I/O device.
When the R/W signal is low, the CPU writes data to a memory or I/O device.
The read and write operations are related, respectively, to the direction of data flow from and to
the CPU.