Instruction manual
Marlin Technical ManualV.2.7.0
160
How does bandwidth affect the frame rate?
How does bandwidth affect the frame
rate?
In some modes the IEEE 1394a bus limits the attainable frame rate. According to
the 1394a specification on isochronous transfer, the largest data payload size of
4096 bytes per 125 μs cycle is possible with bandwidth of 400 Mbit/s. In addi-
tion, 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 For-
mat_7.
If the value for BYTE_PER_PACKET is greater than 4096 (the maximum data pay-
load), 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 based on the following values:
Formula 12: Byte_per_Packet calculation (only Format_7)
Formula 13: Maximum frame rate calculation
Mode bits/pixel byte per pixel
Mono8 8 1
Mono16 16 2
YUV422 16 2
YUV411 12 1.5
Table 77: ByteDepth
BYTE_PER_PACKET frame rate AOIWidth AOIHeight ByteDepth 125μs=
framerate
BYTE_PER_PACKET
AOI_WIDTH AOI_HEIGHT ByteDepth 125μs
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