LM2502 datasheet(24/27 Pages) NSC

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Application Information (Continued)

RGB565 APPLICATION

The LM2502 chipset may also be configured for a RGB565

application. This is also known as a "buffer-less" or "dumb"

display application. In this configuration 16 color bits (R[4:0],

G[5:0], B[4:0]), Pixel Clock (PCLK) and two control bits (VS

and HS) are supported. An external invertor is also required.

To configure for the RGB565 mode, the i80 mode must be

selected. The Pixel clock should be connected to both the

CLK input and the WR* pins on the Master. The PLL_CON

pins should be configured for a 6X mode, as it takes 5 MC

cycles to transfer the RGB data, and the 6X setting will

provide a 50% output PCLK from the Slave device. The 50%

duty cycle PCLK is created by the WR* signal which pulses

low for 3 MC cycles and is high for 2 MC cycles and an idle

MC cycle. See Figure 20 for details. Support is provided for

PCLKs in the 3 to 25 MHz range. PLLCON setting of X8 is

also possible, however, the Slave output PCLK (WR*) will

have some duty cycle distortion (37.5%).

Slower PCLK rates maybe supported if a higher frequency

multiple of the PCLK is available. For example, if a 2MHz

PCLK is required, then a 6MHz CLK (freq locked, not phase)

may be applied to the MST CLK input and the 2MHz PCLK

to the MST WR* signal input. The PLLCON setting should be

selected as 2X (PLLCON[2:0] = 000’b). Once again 5 MC

cycles are required to transfer the pixel data, and the WR*

(PCLK) will be 50% duty cycle. The applied CLK and

PLLCON should be selected such that is creates a 6X

multiple on MC to ensure a 50% duty cycle.

QVGA Example - For a QVGA display (320 by 240), with 16

bits of color depth and 60 frames per second, a net band-

width requirement is 73.728 Mbps. Maximum transfer rate

for the LM2502 chipset is 245 Mbps (307 Mbps raw - in-

cludes overhead), thus there is adequate bandwidth for this

application and even larger resolution displays.

20093301

FIGURE 19. Display Interface Application

20093322

FIGURE 20. RGB565 Application

LM2502 датащи(PDF) 24 Page - National Semiconductor (TI)