Used to Hold fixed code (ex. BIOS), tables of data (ex. FSM next state/output logic), slowly changing values (date/time on computer)
Mask ROM -
- Used with logic circuits for tables etc.
- Contents fixed at IC fab time (truly write once!)
EPROM (erasable programmable) & FLASH
Data sheet for AM27x040
- requires special IC process (floating gate technology)
- writing is slower than RAM. EPROM uses special programming system to provide special voltages and timing.
- reading can be made fairly fast.
- rewriting is very slow.
- erasure is first required
- EPROM - UV light exposure
(because of extra cost of special package, most parts are shipped without erasure option.)