Instruction manual

How does bandwidth affect the frame rate?
11 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 Mb/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.
sByteDepthAoiHeightAoiWidthfpsPACKETPERBYTE
µ
125__ •
•
•
•
=
Formula 7: Byte_per_Packet calculation
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):
sByteoiHeight ⋅⋅ DepthAAoiWidth
PACKETPERBYTE
fps
µ 125
__
⋅
≈
Formula 8: Max. fps Calculation
n the following values:
ytes per pixel
YUV4:1:1 => 12 bits/pixel = 1.5 bytes per pixel
ByteDepth based o
Mono8 => 8 bits/pixel = 1 byte per pixel
Mono16 => 16 bits/pixel = 2 bytes per pixel
YUV4:2:2 => 16 bits/pixel = 2 b
Example formula for the b/w camera:
Mono16, 1392 x 1040 – 15 fps desired
32,11
125210401392
4096
4096542812521040139215__ ⋅⋅⋅⋅=
PACKETPERBYTE
=
⋅⋅⋅
≈⇒
>=
s
fps
s
reachable
µ
µ
Formula 9: Example max. fps calculation
MARLIN Technical Manual
Page 126