LCD Controller Registers
11-45
LCD Controller
All of these factors alter the time duration from one frame transmission to the
next. Different display manufacturers require different frame refresh rates,
depending on the physical characteristics of the display. The PCD is used to
alter the pixel clock frequency in order to meet these requirements. The PCD
is also used in parallel data input mode to select the frequency of pixel clock.
Pixel clock is used to synchronously signal the off-chip device to drive data to
the LCD data pins and to signal the output FIFO to latch the data from the pins.
The frequency of the pixel clock for a set PCD value or the required PCD value
to yield a target pixel clock frequency can be calculated using the following
equation:
Pixel Clock = LCD_CK/PCD
The pixel clock frequency can be programmed with the following limitations.
Table 11–21. Minimum Pixel Clock Divider (PCD)
Type of Display
Output (Number
of Signals)
Minimum Pixel Clock Divider
Active
16 (1 pixel/clock)
2
Monochrome
4 (4 pixels/clock)
4
Passive color
8 (2
2/3
pixels/clock)
3
11.8.5 LCD Status Register (LcdStatus)
The LCD controller status register (LCSR) contains bits that signal overrun
and underrun errors for the input and output FIFOs and the ac-bias pin transi-
tion count, LCD disabled, DMA base update ready, and DMA transfer bus error
conditions. Each of these hardware-detected events signals an interrupt
request to the interrupt controller.
Each of the LCD status bits signals an interrupt request as long as the bit is
set. Once the bit is cleared, the interrupt is cleared. Read/write bits are called
status bits; read-only bits are called flags. Status bits are referred to as sticky
(that is, once set by hardware, they must be cleared by software). Writing 1 to
a sticky status bit clears it; writing zero has no effect. Read-only flags are set
and cleared by hardware; writes have no effect.
Table 11–22 describes the LCD status register (LcdStatus) bits.
See Table 11–23 for the location of the bit fields located in LCD subpanel
register and provides bit descriptions.