¡ Semiconductor
ML9041
Character Generator RAM (CGRAM)
The CGRAM is used to generate user–specific character patterns that are not in the CGROM.
CGRAM (64 bytes = 512 bits) can store up to 8 small character patterns (5 ¥ 8 dots) or up to 4 large
character patterns (5 ¥ 11 dots).
When displaying a character pattern stored in the CGRAM, write an 8–bit character code (00 to
07 or 08 to 0F; hex.) assigned in Table 2 to the DDRAM. This enables outputting the character
pattern to the LCD display position corresponding to the DDRAM address.
The cursor or blink is also displayed even when a CGRAM or ABRAM address is set in the ADC.
Therefore, the cursor or blink display should be inhibited while the ADC is holding a CGRAM
or ABRAM address.
The following describes how character patterns are written in and read from the CGRAM.
1) Small character patterns (5 ¥ 8 dots) (See Table 3–1.)
(1) A method of writing character patterns to the CGRAM from the CPU
The three CGRAM address bits 0 to 2 select one of the lines constituting a character pattern.
First,setthemodetoincrementordecrementfromtheCPU,andtheninputtheCGRAMaddress.
Write each line of the character pattern code in the CGRAM through DB to DB .
0
7
The data lines DB0 to DB7 correspond to the CGRAM data bits 0 to 7, respectively (see Table 3.1).
Input data “1” represents the ON status of an LCD dot and “0” represents the OFF status. Since
the ADC is automatically incremented or decremented by 1 after the data is written to the
CGRAM, it is not necessary to set the CGRAM address again.
The bottom line of a character pattern (the CGRAM address bits 0 to 2 are all “1”, which means
7 in hexadecimal) is the cursor line. The ON/OFF pattern of this line is ORed with the cursor
pattern for displaying on the LCD. Therefore, the pattern data for the cursor position should be
all zeros to display the cursor.
Whereas the data given by the CGRAM data bits 0 to 4 is output to the LCD as display data, the
data given by the CGRAM data bits 5 to 7 is not. Therefore, the CGRAM data bits 5 to 7 can be
used as a RAM area.
(2) A method of displaying CGRAM character patterns on the LCD
The CGRAM is selected when the higher–order 4 bits of a character code are all zeros. Since bit
3 of a character code is not used, the character pattern “0” in Table 3–1 can be selected using the
character code “00” or “08” in hexadecimal.
When the 8–bit character code corresponding to a character pattern in the CGRAM is written to
the DDRAM, the character pattern is displayed in the display position specified by the DDRAM
address. (The DDRAM data bits 0 to 2 correspond to the CGRAM address bits 3 to 5,
respectively.)
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