Datasheet

 1997 Microchip Technology Inc. DS30444E - page 95
PIC16C9XX
13.1 LCD Timing
The LCD module has 3 possible clock source inputs
and supports static, 1/2, 1/3, and 1/4 multiplexing.
13.1.1 TIMING CLOCK SOURCE SELECTION
The clock sources for the LCD timing generation are:
• Internal RC oscillator
• Timer1 oscillator
• System clock divided by 256
The first timing source is an internal RC oscillator which
runs at a nominal frequency of 14 kHz. This oscillator
provides a lower speed clock which may be used to
continue running the LCD while the processor is in
sleep. The RC oscillator will power-down when it is not
selected or when the LCD module is disabled.
The second source is the Timer1 external oscillator.
This oscillator provides a lower speed clock which may
be used to continue running the LCD while the proces-
sor is in sleep. It is assumed that the frequency pro-
vided on this oscillator will be 32 kHz. To use the
Timer1 oscillator as a LCD module clock source, it is
only necessary to set the T1OSCEN (T1CON<3>) bit.
The third source is the system clock divided by 256.
This divider ratio is chosen to provide about 32 kHz
output when the external oscillator is 8 MHz. The
divider is not programmable. Instead the LCDPS regis-
ter is used to set the LCD frame clock rate.
All of the clock sources are selected with bits CS1:CS0
(LCDCON<3:2>). Refer to Figure 13-1 for details of the
register programming.
FIGURE 13-8: LCD CLOCK GENERATION
CS1:CS0
TMR1 32 kHz
crystal oscillator
Internal RC oscillator
Nominal F
RC = 14 kHz
Static
1/2
1/3
1/4
÷4
÷32
LMUX1:LMUX0
4-bit Programmable
LCDPS<3:0>
÷1,2,3,4
Ring Counter
LMUX1:LMUX0
internal
data bus
COM2
÷256
÷2
FOSC
Prescaler
COM0 COM1 COM3