Intel PXA255 - Manual (Page 288)

7-26 Intel® PXA255 Processor Developer’s Manual
LCD Controller
7.6.3 LCD Controller Control Register 2 (LCCR2)
LCCR2, shown in Table 7-5 , contains four bit fields that are used as values for a collection of down
counters, each of which performs a different function to control the timing of several of the LCD’s
pins.
Beginning-of-Frame Line Clock Wait Count (BFW) — used in active mode (LCCR0[PAS] = 1)
to specify the number of line clocks to insert at the beginning of each frame. The BFW count starts
when the VSYNC signal for the previous frame is negated. The value in BFW is used to count the
number of line clock periods to insert before starting pixel output in the next frame. BFW generates
a wait period ranging from 0 to 255 extra L_LCLK cycles (BFW=0x00 disables the wait count).
L_LCLK does toggle during the generation of the BFW line clock wait periods.
In passive mode, BFW must be set to zero so that no beginning-of-frame wait states are generated.
Use VSW exclusively in passive mode to insert line clock wait states, which allow the LCD
controller’s DMAC to fill the palette and insert additional pixels before the start of the next frame.
End-of-Frame Line Clock Wait Count (EFW) — used in active mode (LCCR0[PAS] = 1) to
specify the number of line clocks to insert at the end of each frame. Once a complete frame of
pixels is transmitted to the LCD display, the value in EFW is used to count the number of line clock
periods to wait. After the count has elapsed, the VSYNC (L_FCLK) signal is pulsed. EFW
generates a wait period ranging from 0 to 255 line clock cycles (EFW = 0x00 disables the EOF
wait count). L_LCLK does not toggle during the generation of the EFW line clock periods.
Table 7-4. LCCR1 Bit Definitions
Physical Address
0x4400_0004
LCD Controller Control Register 1 LCD Controller
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
BLW ELW HSW PPL
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
31:24 BLW
Beginning-of-Line pixel clock Wait count:
Value (0–255) specifies the number of pixel clock periods to add to the beginning of a line
transmission before the first set of pixels is sent to the display. BOL wait = (BLW + 1).
23:16 ELW
End-of-line pixel clock wait count:
Value (0–255) specifies the number of pixel clock periods to add to the end of a line
transmission before line clock is asserted. EOL = (ELW+1).
In passive display mode, Pixel Clock is held in its inactive state during the end-of-line wait
period. In active display mode, it toggles.
15:10 HSW
Horizontal sync pulse width:
Value (0–63) specifies the number of pixel clock periods to pulse the line clock at the end of
each line. HSYNC pulse width = (HSW+1).
In passive display mode, Pixel Clock is held in its inactive state during the generation of the
line clock. In active display mode, it toggles.
9:0 PPL
Pixels per line:
Specifies the number of pixels contained within each line on the LCD display. Actual pixels
per line = (PPL+1).