A-Level Physics AQA 7408

Combinational logic

Use of Boolean algebra related to truth tables and logic gates.

$\bar{a} = \bold{not}~A$

$A ⋅ B = A~\bold{and}~B$

$A + B = A~\bold{or}~B$

Identification and use of AND, NAND, OR, NOR, NOT and EOR gates in combination in logic circuits.

Construction and deduction of a logic circuit from a truth table.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

Sequential logic

Counting circuits:

• Binary counter
• BCD counter
• Johnson counter.

Inputs to the circuits, clock, reset, up/down.

Outputs from the circuits.

Modulo-n counter from basic counter with the logic driving a reset pin.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

Astables

The astable as an oscillator to provide a clock pulse.

Clock (pulse) rate (frequency), pulse width, period, duty cycle, mark-to-space ratio.

Variation of running frequency using an external RC network.

Knowledge of a particular circuit or a specific device (eg 555 chip) will not be required.