Tutorials - Elettronica

 
 

Dot matrix LCD : the CGRAM


What to write in CGRAM.

We observed that the content of CGRAM must correspond to the matrix of points on or off that you want to present on the display.

For example, to obtain the display of a symbol designed ad hoc:

Locazione Punti Contenuto
binario hex
1 0 1 1 1 0 01110 0Eh
2 1 0 0 0 1 10001 11h
3 1 0 0 0 1 10001 11h
4 0 1 1 1 0 01110 0Eh
5 0 0 1 0 0 00100 04h
6 0 0 1 0 0 00100 04h
7 0 0 1 0 0 00100 04h
8 0 1 1 0 0 01100 0Ch

you should write the sequence of bytes 04h, 0Eh, 11h, 11h, 0Eh, 04h, 04h, 04h, 0Ch in 8 consecutive locations of CGRAM.

Since the CGRAM is designed to hold 8 symbols of 8 bytes each, each symbol will have a different starting address:

Symbol  Code Relative address
in CGRAM
Space in CGRAM Absolute address 
in RAM
1 00 00h 00 - 07h 40h
2 01 08h 08 - 0Fh 48h
3 02 10h 10 - 17h 50h
4 03 18h 18 - 1Fh 58h
5 04 20h 20 - 27h 60h
6 05 28h 28 - 2Fh 68h
7 06 30h 30 - 37h 70h
8 07 38h 38 - 3Fh 7Fh

For example, the symbol seen above, positioned as symbol 3, will occupy these positions in memory

Indirizzo in CGRAM Contenuto
B7 B6 B5 B4 B3 B2 B1 B0
10h 0 0 0 0 1 1 1 0
11h 0 0 0 1 0 0 0 1
12h 0 0 0 1 0 0 0 1
13h 0 0 0 0 1 1 1 0
14h 0 0 0 0 0 1 0 0
15h 0 0 0 0 0 1 0 0
16h 0 0 0 0 0 1 0 0
17h 0 0 0 0 1 1 0 0

The symbol next location 18h and will start from the next 8 bytes and so on.

The symbol will be called into DDRAM writing code 03h. The next symbol it will be with the code 04h, and so on.

Note that the CGRAM is composed of cells of 8 bits each, of which, however, the symbol in the format 5x8 occupies only the first 5 least significant bits.
 
Bits B5 to B7 are not part of the display and can take any value.


 

 

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Aggiornato il 04/12/12.