PEDL9041A-02
OKI Semiconductor
ML9041A-xxA/xxB
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 bit weights 0 to 2 select one of the lines constituting a character pattern.
First, set the mode to increment or decrement from the CPU, and then input the CGRAM address.
Write each line of the character pattern in the CGRAM through DB0 to DB7.
The data lines DB0 to DB7 correspond to the CGRAM data bit weights 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 bit weights 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 bit weights 0 to 4 is output to the LCD as display data, the
data given by the CGRAM data bit weights 5 to 7 is not. Therefore, the CGRAM data bit weights 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 weight 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 bit weights 0 to 2 correspond to the CGRAM address bit weights 3 to 5, respectively.)
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