Rainbow Electronics MAXQ3120 - Manual (Page 26)

MAXQ3120
LCD Driver
The MAXQ3120 microcontroller incorporates an LCD
driver that interfaces to common low-voltage displays.
By incorporating the LCD driver into the microcon-
troller, the design requires only an LCD glass rather
than a considerably more expensive LCD module.
Every character in an LCD glass is composed of one or
more segments, each of which is activated by selecting
the appropriate segment and common signal. The
microcontroller can drive up to 112 LCD glass seg-
ments by multiplexing combinations of 28 segment
(SEG0–SEG27) outputs and four common-signal out-
puts (COM0–COM3). Eight of the segment outputs can
also be used as general-purpose port pins, if they are
not needed to drive the LCD.
The segments are easily addressed by writing to dedi-
cated display memory. Once the LCD driver settings
and display memory have been initialized, the 14-byte
display memory is periodically scanned, and the seg-
ment and common signals are generated automatically
at the selected display frequency. No additional proces-
sor overhead is required while the LCD driver is running.
Unused display memory can be used for general-pur-
pose storage.
The design is further simplified and cost-reduced by
the inclusion of software-adjustable internal voltage-
dividers to control display contrast. If desired, contrast
can also be controlled by an external resistance. The
features of the LCD driver include the following:
• Automatic LCD segment and common-drive signal
generation
• Four display modes supported:
Static (COM0)
1/2 duty multiplexed with 1/2 bias voltages
(COM0, COM1)
1/3 duty multiplexed with 1/3 bias voltages
(COM0, COM1, COM2)
1/4 duty multiplexed with 1/3 bias voltages
(COM0, COM1, COM2, COM3)
• Up to 28 segment outputs and four common-signal
outputs
• 14 bytes (112 bits) of display memory
• Adjustable frame frequency
• Internal voltage-divider resistors eliminate require-
ment for external components
• Internal adjustable resistor allows contrast adjust-
ment without external components
• Flexibility to use external resistors to adjust drive
voltages and current capacity
A simple LCD-segmented glass interface example
demonstrates the minimal hardware required to inter-
face to a MAXQ3120 microcontroller. A two-character
LCD is controlled, with each character containing
seven segments plus decimal point. The LCD driver is
configured for 1/2 duty cycle operation, meaning the
active segment is controlled using a combination of
segment signals, and COM0 or COM1 signals are used
to select the active display.
High-Precision ADC
Mixed-Signal Microcontroller
26 ____________________________________________________________________
Figure 5. Two-Character, 1/2 Duty, LCD Interface Example
SEG0
SEG1
SEG2
SEG3
COM0
SEG0:7
CONNECTED TO DARK GREY SEGMENTS
COM1 CONNECTED TO LIGHT GREY SEGMENTS
SEG4
SEG5
SEG6
SEG7
MAXQ3120