Character generator.

摘要

The character generator includes two memories (10, 12) and two access means (16, 18). A first memory comprises a resident area (10A) for permanently storing a plurality of character patterns of high frequency of use, and an overlay area (10B) for storing a plurality of requested character patterns not found in the resident area. The contents of the overlay area can be replaced, if necessary. A second memory (12) permanently stores all character patterns and transfers requested character patterns to the first memory (10). Any character pattern stored in the resident area of the first memory is accessed by a first access means (16) based on a fixed relation between an input code point representing a requested character pattern and a storage location thereof. Any character pattern stored or to be stored in the overlay area (10B) of the first memory (10) is accessed by a second access means using a hash table and a character directory containing a plurality of chains of character information. Each valid entry of the character directory corresponds to a particular character pattern in the overlay area. The character directory is updated to reflect usage status of character patterns in the overlay area whenever the directory is accessed by the hash table.