CL-PS7111-VC-A View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CL-PS7111-VC-A

Low-Power System-on-a-Chip

Cirrus Logic 

CL-PS7111

Low-Power System-on-a-Chip

Bit Description (cont.)

24:19 Pixel Prescale: The pixel prescale field is a 6-bit field that sets the pixel rate prescale. The pixel rate is derived from a

36.864-MHz clock and is calculated with Equation 5-2.

Pixel rate (MHz) = 36.864 ÷ (pixel prescale + 1)

Equation 5-2

The pixel rate should be chosen to give a complete screen refresh frequency of approximately 70 Hz to avoid flicker.

Frequencies above 70 Hz should be avoided as they consume additional power. The pixel prescale value can be

expressed in terms of the LCD size by using Equation 5-3.

Pixel prescale = (526628 ÷ Total pixels in display) − 1

Equation 5-3

The value should be rounded down to the nearest whole number. ‘0’ is illegal and results in no pixel clock.

For example:

A 640 × 240 LCD, pixel prescale = 526628 ÷ (640 × 240) − 1 = 2.428 (2)

Equation 5-4

Equation 5-4 gives an actual pixel rate of 36.864E6 ÷ 2 + 1 = 12.288 MHz, which gives an actual refresh frequency of

12.288E6 ÷ (640 × 240) = 80 Hz.

NOTE: As the CL2 low pulse time is doubled after every CL1 high pulse (see Figure 6-8 on page 86), this refresh fre-

quency is only an approximation; the accurate formula is shown in Equation 5-5.

12.288E6 ÷ ((640 × 240) + 120) = 79.937 Hz.

Equation 5-5

18:13 Line Length: The line length field is a 6-bit field that sets the number of pixels in one complete line. This field is calcu-

lated with Equation 5-6.

Line length = (No. pixels in line ÷ 16) - 1

Equation 5-6

For example, for 640 × 240 LCD Line length = (640 ÷ 16) − 1 = 39 or 0x27 h.

NOTE: The minimum value that can be programmed into this register is ‘1’ (that is, ‘0’ is not a legal value).

12:0 Video Buffer Size: The video buffer size field is a 13-bit field that sets the total number of bits × 128 (quad words) in

the video display buffer. This is calculated with Equation 5-7.

Video buffer size = (Total bits in video buffer / 128) - 1

Equation 5-7

For example, for a 640 × 240 LCD and 4 bits per pixel the size of the video buffer = 640 × 240 × 4 = 614400 bits

Video buffer size field = (614400 ÷ 128) − 1 = 4799 or 0x12BF h.

Equation 5-8

September 1997

PRELIMINARY DATA BOOK v2.0

61

REGISTER DESCRIPTIONS

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