參數(shù)資料
型號: BT848A
英文描述: Single-Chip Video Capture for PCI
中文描述: 單芯片的PCI視頻捕捉
文件頁數(shù): 55/141頁
文件大?。?/td> 1149K
代理商: BT848A
Brooktree
45
F
UNCTIONAL
D
ESCRIPTION
Video and Control Data FIFO
L848A_A
Bt848/848A/849A
Single-Chip Video Capture for PCI
The DMA Controller will guarantee that the FIFO does not fill, therefore the
VDFC has no responsibility for FIFO overruns. The DMA Controller will be able
to resynchronize to data streams that are shorter or longer than expected.
Note that planar mode and packed mode data can be present in the FIFOs at the
same time if a bus access latency persists across a FIELD transition, or if packed
VBI data proceeds planar YCrCb data.
Physical Implementation
The three FIFO outputs are delivered in parallel so that the DMA Controller can
monitor the FIFOs and perform skipping (reading and discarding data), if neces-
sary, on all three simultaneously.
Due to the latency in determining the number of DWORDs placed in each
FIFO, a FIFO Full (FFULL) condition is indicated prior to the FIFO count reach-
ing the maximum FIFO size. The FIFO is considered FFULL when the FIFO
Count (FCNT) value equals or exceeds the FFULL value.
A read must occur on the same cycle as FFULL, otherwise data will overflow
and will be overwritten. The maximum bus latencies for various video formats and
modes are shown in Table 10.
FIFO Input/Output Rates
The input and output ports of the Bt848’s FIFO can operate simultaneously and are
asynchronous to one another.
The maximum FIFO input rate would be for consecutive writes of PAL video at
17.73 MHz. However, there will never be consecutive-pixel-cycle writes to the
same FIFO. The fastest FIFO write sequence is F1, F2, F1, F3. Therefore, the fast-
est write rate to any FIFO is less than or equal to half of the pixel rate.
The maximum FIFO output read rate is one FIFO word at the PCI clock rate (33
MHz). All three FIFOs can be read simultaneously. Some bus systems may be de-
signed with PCI clocks slower than 33 MHz. The Bt848 data FIFO only supports
systems where the maximum input data rate is less than the output data rate. It can
support a input video clock (17.73 MHz) faster than the PCI clock (16 MHz) as
long as the video data rate does not exceed the available PCI burst rate.
FSIZE1 = 70
FSIZE2 = 35
FSIZE3 = 35
FSIZET = 140
FFULL1 = 68
FFULL2 = 34
FFULL3 = 34
FFULLT = 136
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