Instruction manual

Guppy Technical ManualV7.4.0
193
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, there is a limitation, only a maximum number of 65535 (2
16
-1) packets per
frame are allowed (Guppy F-036: max. number of 800 packets due to the sensor
limitation).
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 9: Byte_per_Packet calculation (only Format_7)
Formula 10: Maximum frame rate calculation
Mode Bits/pixel Byte per pixel
Mono8 8 1
RAW8 8 1
Table 84: ByteDepth
BYTE_PER_PACKET frame rate x AOIWidth x AOIHEIGHT x ByteDepth x 125μs=
framerate
max
BYTE_PER_PACKET
AOIWidth x AOIHeight x ByteDepth x 125μs
------------------- --------------------- ---------------------- --------------------------- --------------
