83Plus:RAM:8447

Synopsis

Official Name: contrast

Memory Address: 8447h

Length: 1 byte

This area holds the system contrast value. When you press 2nd+Up or 2nd+Down while in a GetKey, GetKey automatically increases or decreases this value and updates the LCD's contrast. The accepted range of this value is 00h ~ 27h.

Comments

Changing this value does not "instantly" update the LCD contrast; you must manually update the LCD. To set the LCD contrast to match the calculator's, add D8h to the read value and output to Port 10h:

ld a, (contrast)
add a, 0D8h
CALL 000Bh ; Wait for LCD driver to be ready
out (10h), a

This simple routine sets both the system contrast and the LCD contrast to whatever is in A (valid range is 00~27h, does nothing if out of range).

cp 28h
ret nc ; return if the value given is >= 28h
ld (contrast), a
push af
add a, 0D8h
CALL 000Bh ; Wait for LCD driver to be ready
out (10h), a
pop af
ret