LCD & VGA Controllers
11-20
GMS30C7201 Data Sheet
11.11LCD Controller Status/Mask and Interrupt Registers
The LCD controller status, mask and interrupt registers all have the same format. Each
bit of the status register is a status bit that may generate an interrupt. These are
masked by the corresponding bits in the mask register. The interrupt register is the
logical AND of the status and mask registers, and the interrupt output from the LCD
controller is the logical OR of the bits within the interrupt register.
The LCD controller status register (LCSR) contains bits that signal an under-run error
for the FIFO, the DMA next base update ready status, and the DMA done status. Each
of these hardware-detected events can generate an interrupt request to the interrupt
controller.
11.11.1LCD Frame Done (LDone)
The LCD Frame Done (Done) is a read-only status bit that is set after the LCD has been
disabled and the frame that is active finishes being output to the LCD
’
s data pins. It is
cleared by writing the base address (
LcdDBAR
) or enabling the LCD, or, by writing
“
1
”
to the LDone bit of the Status Register. When the LCD is disabled by clearing the LCD
enable bit (
LcdEn
=0) in LcdControl, the LCD allows the current frame to complete
before it is disabled. After the last set of pixels is clocked out onto the LCD
’
s data pins
by the pixel clock, the LCD is disabled and Done is set.
11.11.2LCD Next Frame (LNext)
The LCD Next Frame (LNext) is a read-only status bit that is set after the contents of
the LCD DMA base address register are transferred to the LCD DMA current address
register, and it is cleared when the LCD DMA base address register is written.
11.11.3FIFO Underflow Status (LFUF)
The LCD FIFO underflow status (LFUF) status bit is set when the LCD FIFO under-
runs. The status bit is
“
sticky
”
, meaning it remains set after the FIFO is no longer under-
running. The status bit is cleared by writing a
‘
1
’
to this bit of the status register.
11.11.4VComp Interrupt
This bit is set when the Lcd timing generator reaches the vertical region programmed
in the Video Control Register. This bit is
“
sticky
”
, meaning it remains set until it is
cleared by writing a
“
1
”
to this bit of the status register.
Bit
Name
Description
0
LFUF
FIFO underflow status/mask/interrupt bit
1
LNext
LCD Next base address update status/mask/interrupt bit
This status bit is set when the base address is transferred to the
current address register at the start of frame
2
VComp
Vertical compare interrupt
3
LDone
LCD Done frame status/mask/interrupt bit
This status bit is set when
LcdEn
has been set to
‘
0
’
, after the
current frame completes
Table 11-11: LCD Controller Status/Mask and Interrupt Registers