W99681CF Datasheet, PDF (34/78 Pages) Winbond – JPEG USB Dual Mode Camera Chip

W99681CF
7.5 Video/Still Image Data Transfer
Video or still image data from the device is delivered to the host system through an isochronous pipe
(Endpoint 1). The maximum packet size can be varied for different alternate settings for limited USB
bandwidth for other USB devices.
7.5.1 Output Video Data Format
The W99681CF supports two video transfer modes: original video transfer mode and JPEG
compression video transfer mode. The captured video stored in the DRAM will be compressed by the
JPEG encoder and then transferred to the host if JPEG compression video transfer mode is selected,
or will be directly transferred to the host if original video transfer mode is selected. Four different
formats are supported for the output video which are selected by bits 1-0 of the Video Capture Control
register (CR26) and bits 1 of the JPEG Encoder Control register (CR39) as described in Table 7.13.
Table 7.13 Output Video Data Format
CR39_1 CR26_1-0 Output Video Data Format
0
00
Original YUV4:2:2 packed mode
0
01
Original YUV4:2:0 packed mode
1
0X
Reserved
1
10
JPEG YUV4:2:2 non-interleaved scan mode
1
11
JPEG YUV4:2:0 non-interleaved scan mode
7.5.2 Video Frame Synchronization
A single video frame typically requires multiple USB packets. One or more zero length isochronous
data packets are used to mark the end of a video frame. The first non-zero data packet is the start of
the next video frame.
If an error is encountered during the reception of a USB packet, the host may discard the entire video
frame. Processing begins again with the next video frame as indicated by the first non-zero length
isochronous data packet after one or more zero-length packet.
7.5.3 Bandwidth Management
The W99681CF provides for varying the bandwidth required by providing a zero-bandwidth interface
(alternate setting zero) and 16 alternate settings interfaces with 8 Mbps down to 0.5 Mbps bandwidth in
descending 0.5 Mbps steps. The default alternate setting zero (with zero bandwidth) selected by a Set
Configuration request allows a video camera to be initially configured even on a highly utilized USB bus.
Before the device begins streaming video data, the host software must select an alternate setting with
the appropriate amount of bandwidth by using the Set Interface request.
- 34 -