The on-board CMOS has a built-in two page, 256 character ROM. Both pages are mask programmable for 256 custom characters. The first page of ROM of the standard product contains 128 characters including ASCII, selected European and Scientific symbols. The second page contains Katakana Japanese characters, more European characters, Avionics, and other graphic symbols. The PLCD558X is designed for standard microprocessor interface techniques and is fully TTL compatible. The Clock I/O and Clock Select pins allow the user to synchronize multiple display modules.