Multibit rom memory

A memory reading circuit for reading a ROM device, wherein

• said ROM device comprises a set of memory points arranged in rows and columns, each memory point capable of storing two bits of data and comprising a single switch controllable to connect together first and second terminals of said switch, each of said first and second terminals being connected to one of first, second and third conductive lines, said memory reading circuit comprising:
• a first switch arranged to connect said first line to one of a first output node and a first voltage level;
• a second switch arranged to connect said second line to one of a second output node and said first voltage level;
• and
• precharging means arranged to store a second voltage level on a selected one of said first and second lines.

A method of encoding data in a ROM device, comprising memory points arranged in rows and columns, each column further comprising three conductive lines, each memory point storing two bits of data and comprising a controllable switch comprising first and second main terminals, said method comprising:

• independently connecting said first and second terminals to said first, second and third lines to encode said data, wherein connecting said first terminal to said first line and said second terminal to said second line encodes a first data value;
• connecting said first terminal to said first line and said second terminal to said third line encodes a second data value;
• connecting said first terminal to said second line and said second terminal to said third line encodes a third data value;
• and connecting said first and second terminals to a same one of said first, second and third lines encodes a fourth data value.

A method of decoding data from a ROM device comprising a set of memory points arranged in rows and columns, each memory point capable of storing two bits of data and comprising a single switch controllable to connect together first and second terminals of said switch, each of said first and second terminals being connected to one of first, second and third conductive lines, the method comprising the steps of:

• connecting said second and third lines to a first voltage level;
• storing a second voltage level on said first line;
• activating one of said memory points;
• and
• detecting the voltage on said first line and determining a first bit of said data based on only the voltage detected on the first line.