Computer Architecture Flashcards
What are the main forms of signal by which data can be taken in or out of a computer?
Digital Data. Binary number represents a physical value.
Analogue Data. Varying voltage or current.
Trains of pulses. The rate form of digital data.
Describe the TTL Open Collector.
Instead of 2 transistors. 1 transistor on output circuit.
That transistor connects the output to ground or leaves it floating.
The output is connected to a power supply.
When the logic gate is operated, output is either pulled up to the external voltage, or is pulled down to the ground via open collector circuiting, shorting output to the ground.
Open collector more versatile than totem pole as output can be in any reasonable desired range.
What is the CMOS version of Open Collector?
Open drain.
What happens if one connects directly to the data bus in an attempt to transfer data from an external device?
Varying voltages would swamp data, causing corruption and the computer to stop.
What is a Tri-State Buffer used for?
To overcome the swamping and corruption of data when transferring data from an external device to the data bus.
Describe how a Tri-State Buffer works.
It has three states: High, low and high impedance.
Initially, all outputs from the buffer are high impedance and the data bus is not interfered with.
The buffer is only enabled at the instant we want to transfer data from an external device to the bus.
The bus is set to the same values as the input lines and data is transferred.
When the buffer is disabled, the output is high impedance once more and it disconnects from the bus.
Needs address decoder,
What is a Latch used for?
Accessing data from the PC.
Describe how a Latch works.
The data is only present of the data bus for a fraction of a second.
The values on the data bus must be latched at a given instant to allow data to be copied to the outside world.
When the latch is enabled, data is copied from the data bus.
When the latch is disabled, the last piece of data on the data bus at that instant is frozen to the output latch.
What are Registers?
A much quicker way of dealing with input or output facilities.
They are memory mapped locations containing: Digital Input/Output Ports, Control Registers.
Register level programming can run much faster.
