Intel SA-1100 manual Lines Per Panel LPP, Vertical Sync Pulse Width VSW, 11-36

Peripheral Control Module

11.7.5LCD Controller Control Register 2

LCD controller control register 2 (LCCR2) contains four bit fields that are used as modulus 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.

11.7.5.1Lines Per Panel (LPP)

The lines per panel (LPP) bit field is used to specify the number of lines or rows present on the LCD panel being controlled. In single-panel mode, it represents the total number of lines for the entire LCD display. In dual-panel mode, it represents half the number of lines of the entire LCD display because it is split into two panels. LPP is a 10-bit value that represents between 1 and 1024 lines per screen.

The user should program LPP with the desired height of the display minus one. LPP is used to count the correct number of line clocks that must occur before the frame clock can be pulsed.

The LCD’s DMA may overshoot the end of frame buffer by one burst cycle (4-word read). The LCD’s DMA reads these extra values but they are flushed from the input FIFO each time the frame clock is pulsed. The user must ensure that the four words immediately following the end of the frame buffer reside in legal memory space (do not cause a bus error if read). Because the LCD does not alter this memory (only reads are performed), these locations can be used for data storage unrelated to the LCD.

11.7.5.2Vertical Sync Pulse Width (VSW)

The 6-bit vertical sync pulse width (VSW) field is used to specify the pulse width of the vertical synchronization pulse in active mode, or is used to add extra “dummy” line clock waitstates between the end and beginning of frame in passive mode.

In active mode (PAS=1), L_FCLK is used to generate the vertical sync signal and is asserted each time the last line or row of pixels for a frame is output to the display and a programmable number of line clock waitstates have elapsed as specified by ELW. When L_FCLK is asserted, the value in VSW is transferred to a 6-bit down counter, which uses the line clock frequency to decrement.

When the counter reaches zero, L_FCLK is negated. VSW can be programmed to generate a vertical sync pulse width ranging from 1 to 64 line clock periods. The user should program VSW with the desired number of line clocks minus one. Note that the line clock does not transition during generation of the vertical sync pulse. Also note that the polarity (active and inactive state) of the L_FCLK pin is programmed using the frame clock polarity (FCP) bit in LCCR3.

In passive mode (PAS=0), VSW does not affect the timing of the L_FCLK pin, but rather can be used to add extra line clock waitstates between the end of each frame and the beginning of the next frame. When the last line clock of a frame is negated, the value in VSW is transferred to a 6-bit down counter that uses the line clock frequency to decrement. When the counter reaches zero, the next frame is permitted to begin. VSW can be programmed to generate from 1 to 64 dummy line clock periods between each frame in passive mode. The user should program VSW properly to ensure that enough waitstates occur between frames such that the LCD’s DMA is able to fully load the on-chip palette, as well as allowing a sufficient number of encoded pixel values to be input from the frame buffer, to be processed by the dither logic, and placed in the output FIFO, ready to be output to the LCD’s data pins. The number of waitstates required is system dependent. The factors that determine the number of waitstates include: palette buffer size (32 or 512 bytes), memory system speed (number of waitstates, burst speed, number of beats), and what value is programmed in the palette DMA request delay (PDD) bit-field in LCCR0. Note that the line clock pin does transition during the insertion of the line clock waitstate periods.

11-36 SA-1100 Developer’s Manual