PIC16C925-SSLASHCL datasheet(91/182 Pages) MICROCHIP

91 / 182 page

 2001 Microchip Technology Inc.

Preliminary

DS39544A-page 89

PIC16C925/926

11.1

LCD Timing

The LCD module has 3 possible clock source inputs

and supports static, 1/2, 1/3, and 1/4 multiplexing.

11.1.1

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 Register 11-1 for details of

the register programming.

FIGURE 11-6:

LCD CLOCK GENERATION

CS1:CS0

TMR1 32 kHz

Crystal Oscillator

Internal RC Oscillator

Nominal FRC = 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

÷256

÷2

FOSC

Prescaler

CPCLK

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