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How does bandwidth affect the frame rate?
OSCAR Technical Manual V2.4.0
142
How does bandwidth affect the frame
rate?
In some modes the IEEE 1394a bus limits the attainable frame rate. Accord-
ing to the 1394a specification on isochronous transfer, the largest data pay-
load size of 4096 bytes per 125 µs cycle is possible with bandwidth of
400 Mbit/s. In addition, because of a limitation in an IEEE 1394 module
(GP2Lynx), only a maximum number of 4095 packets per frame are allowed.
The following formula establishes the relationship between the required
Byte_Per_Packet size and certain variables for the image. It is valid only for
Format_7.
If the value for BYTE_PER_PACKET is greater than 4096 (the maximum data
payload), the sought-after frame rate cannot be attained.
The attainable frame rate can be calculated using this formula:
(Provision: BYTE_PER_PACKET is divisible by 4):
ByteDepth is based on the following values:
Formula 12: Byte_per_Packet calculation (only Format_7)
Formula 13: Maximum frame rate calculation
Mode bit/pixel byte per pixel
Mono8 8 1
Mono16 16 2
YUV4:2:2 16 2
YUV4:1:1 12 1.5
RGB8 24 3
Table 61: ByteDepth
BYTE_PER_PACKET Framerate AOIWidth× AOIHeight× ByteDepth× 125µs×=
frame rate
BYTE_PER_PACKET
AOIWidth AOIHeight× ByteDepth× 125µs×
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