Mask Rom Addressing Matrix

# Mask ROM: a Bit Is a Transistor You Chose Not to Draw

the row/column matrix that makes that true, and the dot-matrix font it was built to hold

THE ADDRESSING MATRIX, FABRICATED NOT PROGRAMMED

A mask ROM bit is fixed at fabrication, not programmed afterward — the mask pattern that places or omits a device at each row/column crossing is a one-time design decision.

That is the opposite of EPROM/EEPROM/Flash, where the same addressing idea reads bits that were written electrically, long after the chip left the fab.

THE SAME MATRIX, HOLDING A FONT a 5×7 character-generator ROM cell, each dot a stored bit each row of this glyph is one "row" of the matrix on the left — a 7-row address range per character Three named applications, same mechanism character-generator ROM — one 5×7 (or 8×8) glyph block per character code game-cartridge ROM — fixed program and data, never meant to change microcode control store — the CPU's own fixed control sequences

addressing schemes and applications beyond the 4001 — named, not retold: microprocessor_1971, eprom_eeprom_history

Take mask rom addressing matrix further

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