Microchip Technology DM183037 Data Sheet
2012 Microchip Technology Inc.
DS30575A-page 255
PIC18F97J94 FAMILY
13.5.2
CONTRAST CONTROL
The LCD contrast control circuit consists of a 7-tap
resistor ladder, controlled by the LCDCSTx bits (see
resistor ladder, controlled by the LCDCSTx bits (see
)
FIGURE 13-5:
INTERNAL REFERENCE AND CONTRAST CONTROL BLOCK DIAGRAM
13.5.3
INTERNAL REFERENCE
Under firmware control, an internal reference for the
LCD bias voltages can be enabled. When enabled, the
source of this voltage can be V
LCD bias voltages can be enabled. When enabled, the
source of this voltage can be V
DD
.
When no internal reference is selected, the LCD con-
trast control circuit is disabled and LCD bias must be
provided externally. Whenever the LCD module is inac-
tive (LCDA = 0), the internal reference will be turned
off.
trast control circuit is disabled and LCD bias must be
provided externally. Whenever the LCD module is inac-
tive (LCDA = 0), the internal reference will be turned
off.
13.5.4
VLCDxPE PINS
The VLCD3PE, VLCD2PE and VLCD1PE pins provide
the ability for an external LCD bias network to be used
instead of the internal ladder. Use of the VLCDxPE pins
does not prevent use of the internal ladder.
Each VLCDxPE pin has an independent control in the
LCDREFH register, allowing access to any or all of the
LCD bias signals.
This architecture allows for maximum flexibility in differ-
ent applications. The VLCDxPE pins could be used to
add capacitors to the internal reference ladder for
increasing the drive capacity. For applications where
the internal contrast control is insufficient, the firmware
can choose to enable only the VLCD3PE pin, allowing
an external contrast control circuit to use the internal
reference divider.
the ability for an external LCD bias network to be used
instead of the internal ladder. Use of the VLCDxPE pins
does not prevent use of the internal ladder.
Each VLCDxPE pin has an independent control in the
LCDREFH register, allowing access to any or all of the
LCD bias signals.
This architecture allows for maximum flexibility in differ-
ent applications. The VLCDxPE pins could be used to
add capacitors to the internal reference ladder for
increasing the drive capacity. For applications where
the internal contrast control is insufficient, the firmware
can choose to enable only the VLCD3PE pin, allowing
an external contrast control circuit to use the internal
reference divider.
LCDCST<2:0>
Analog
R
R
R
R
7 Stages
MUX
To Top of
Reference Ladder
Reference Ladder
7
0
3
V
DD
Internal Reference
Contrast Control