Read-only memory with few programming signal lines

DETAILED DESCRIPTION It is accordingly an object of the present invention to enable a PROM to be programmed using only a small number of input signals.
A programmable read-only memory circuit has a programmable read-only memory and a signal-generating circuit.
The signal-generating circuit receives a program signal and activates, in sequence, a control signal, an output enable signal, and a latch signal.
A first register receives and holds data to be stored in the programmable read-only memory.
Responsive to the control signal, a three-state buffer outputs data held in the first register onto a data bus.
The programmable read-only memory receives a chip enable signal which causes it to store data from the data bus.
Responsive to the output enable signal, the programmable read-only memory outputs stored data onto the data bus.
Responsive to the latch signal, a second register receives and holds data present on the data bus.
An equality checker compares the contents of the first and second registers and generates an equal signal indicating whether the two contents are equal.