OF CG RAM
Character Generator (CG) RAM is a useful accessory. It does not
have to be used or attended to during any normal display operation.
CG RAM allows the creation of up to 8 special character or symbols.
Once programmed, the newly formed characters may be accessed as
if they were in the "normal" CG ROM. This ROM contains
192 unchangeable characters. Thus the CG RAM expands the character
representation available to the user.
NOTE: This is a RAM, and must be reprogrammed if display power
is interrupted. If used regularly, programming can be made part
of the initialization routine.
There are two distinct areas of RAM within the display module.
The main area, 80 bytes wide, is dedicated to the display and is
called Display Data (DD) RAM. CG RAM consists of 64 bytes which
range from 40 to 7F (hex), or 4 5x10 (or 5x11) symbols. 40-47 locate
the first, custom 5x7 character. 40 is the top row of this character,
47 is the 8th row. Similarly, 48-4F locate the second CG character,
and 78-7F locate the 8th custom character. The locations 40-7F are
the CG "Programming" locations only. Once programmed,
these special characters are displayed by writing to character font
locations 00-07 (hex). 00 will return that character residing in
locations 40-47, 01 returns 48-4F. etc. (See Font Chart).
While the CG RAM byte is 8 bits wide, only the 5 least significant
bits appear on the LCD. Thus D4 represents the left-most dot and
D0 the right-most dot. To illustrate, loading a CG RAM byte with
1F turns all dots in that row on; loading a byte with 00 turns all
dots off. All 7 or 8 rows must be programmed at each desired CG
Programming procedure is:
a) with RS=0 enter the address of the top row of the character
to be programmed (i.e. 40,48,50, etc.)
b) with RS=1 enter pattern data for row 1 (top row)
c) continue to enter pattern data for rows 2-8; it is not necessary
to enter additional addresses if the module has been initialized
with command 06 (auto increment of cursor).
This procedure may be continued until all CG bytes have been loaded.
The CG RAM can create an attractive, "reverse-video"
3 x 5 pattern. Numerals look especially good in this format. Most
letters can be executed. The limitation of 8 characters can be circumvented
by creating a "library" of custom symbols, each totaling
8, resident in the host system. Eight custom symbols can be displayed
at any ONE time. The CG RAM can be periodically reloaded as display
requirements change. If you reload a CG location which is currently
on the display, the change will be immediately apparent. Displays
employing multiple controllers (ie. 4 x 40, 2 x 80. 4 x 80) may
create 8 symbols per controller. The CG RAM adds interest and flexibility
to the LCD module.