Find the contents of control word 8255 for the following configuration:NOTE:all the ports of A,B and C are input ports(mode 1)
a.3Fh
b.BFh
c.9Fh
d.1Fh
Answers
Answer:
a
Explanation:
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Answer:
Explanation:
Programmable peripheral interface 8255:
A general-purpose programmable I/O device called the PPI 8255 is intended to connect the CPU to external devices such a keyboard, DAC, and ADC. We can program it to follow the instructions. It works with nearly all microprocessors. It has three PORT A, PORT B, and PORT C 8-bit bidirectional I/O ports. Different ports can be designated as input or output functions.
It has 40 pins and uses a +5V regulated power source to function. Port C can operate in BSR (bit set rest) mode or in mode 0 of the input-output mode of 8255. Port C is further separated into two 4-bit ports, port C lower and port C upper. Port B can operate in either input-output mode 0 or mode 1. Port A can operate in input-output mode 0, mode 1, or mode 2.
There are two control groups: control groups A and B. Port A and Port C Upper are in Control Group A. Port C lower and port B make up control group B.
Input /Output mode:
Mode 0: In this mode, all three ports (A, B, and C) can be used as straightforward input or straightforward output functions. There is no interrupt handling capability in this mode.
Handshake I/O mode or strobed I/O mode is mode 1. The port C bits are used for handshake signals prior to actual data transfer in this mode, and either port A or port B can function as a simple input port or simple output port. It can handle interruptions and has latched input and output.
Bi-directional data bus mode, or mode 2. Only port A functions in this mode, and port B can function in either mode 0 or mode 1. Handshake signals are sent across port C's six bits. It can also handle interruptions.
Contents of the control word 8255:
The figure depicts the 8255's control word format. The control word, which describes the input/output capabilities of each port, is the information in the control register. By selecting AD 1 and AD 0 in high condition, that is, both ON, the control word register can be accessed to write the control word.
The correct option is 3Fh
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