TECHNICAL INFORMATIONTECHNICAL INFORMATIONBU Series
Bus Synchronization Mode

4-7-1, Asahigaoka, Hino, Tokyo 191-0065, Japan
URL: http://www.toshiba.co.jp/en/

September 16, 2015

Information contained in this document is subject to change without prior notice.
Copyright © 2015 TOSHIBA TELI CORPORATION, All rights reserved.

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1. Overview
Bus Synchronization mode enables multiple cameras' exposure to be synchronized without
using the hardware trigger signal.
In Bus Synchronization mode, cameras are synchronized with periodical 'Isochronous
Timestamp Packet (ITP)' of USB bus. Isochronous Timestamp Packet (ITP) is used to deliver
timestamps from the host PC to all USB devices. It is multicast by hubs to all of theirdownstream ports.
This technical information describes operating conditions and considerations of Bus
Synchronization mode.
USB3.0 Host Card

USB3.0 Hub
IsochronousTimestampPacket

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2. Functional Description
2.1. Bus Synchronous mode: FrameSynchronization = BusBus Synchronization mode, utilizing timestamps of USB bus, is a function to synchronize
exposure of the multiple cameras connected to the same bus.
It enables multiple cameras' exposure to be synchronized without using the hardware trigger
signal.
Bus Sync Mode
Exposure
Camera A

Camera B

Camera C

2.2. Internal Synchronous mode: FrameSynchronization = Off
In Internal Synchronous mode, each camera works with individual timing, exposure is notsynchronized.
Internal Sync Mode
Exposure
Camera A

Camera B

Camera C

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3. Operating Conditions
3.1. Camera Model
The camera models to be synchronized do not necessarily have to be same.
It is just required to adjust cameras' frame rate to the slowest one.
For example, if you want to synchronize BU030 (MAX125fps) and BU130 (MAX30fps), adjust
both cameras' frame rate to less than 30fps.

3.2. Trigger Mode
Bus Synchronization mode operates in Normal Shutter mode (TriggerMode = Off).
In Random Trigger Shutter mode, trigger input signal has priority (TriggerMode = On)

3.3. Exposure TimeExposure time should be shorter than frame rate period.
Each camera can have different exposure time. At this time, the end of exposure issynchronized.
Bus Sync ModeExposure
Camera ACamera B

Camera C

3.4. Bus Topology
3.4.1. Single-host controller card with multiple ports
Cameras connected to different port can be synchronized.
The time difference between each port is about 200 to 300 ns.
The time jitter is a few tens of ns.
1chip 4port Host Card
Delay 200 to 300ns
Jitter a few tens of nsednizohrncyS

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3.4.2. Using Hubs
You can also use the USB Hubs when you want to connect more cameras.
The time delay of the USB Hubs is also about 200 to 300 ns per hub.
1chip 4port Host Card + 4port Hub

Delay +200 to 300ns / hub

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3.4.3. Multiple-host controller card (e.g. 4 host x 4 port card）
Cameras connected to different port cannot be synchronized.
Each host has an individual timestamp.
4chip 4port Host Carddiz enohrncys
UnNote:In Intel's native support USB3.0 Host Controller (any hubs other than the root hub is notinterposed), each port has same timestamp.
Cameras connected to different port can be synchronized and achieve 400MByte/s
respectively.
For more information, please contact our sales representative.

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4. Considerations
4.1. Bus Bandwidth
In the end, all cameras are connected to single host controller in Bus Synchronization mode.
The total bus bandwidth should be controlled less than 400Mbyte/s (depending on the hostcontroller's performance).
For example, if you want to run three BU406M, Bus Synchronization does not work at default
90fps setting because the bus bandwidth overflows (1080Mbyte/s in total).

Bandwidth
Overflow

4Mpixel x 90fps = 360MByte/s

4Mpixel x 90fps = 360MByte/s

4Mpixel x 90fps = 360MByte/s
Total = 1080MByte/s

To solve this bandwidth overflow, the frame rate setting should be lowered to 30fps.
The total required bandwidth will be reduced to 360MByte/s. Then, Bus Synchronization willwork.

BusSync
Operation
Available4Mpixel x 30fps = 120MByte/s

4Mpixel x 30fps = 120MByte/s

4Mpixel x 30fps = 120MByte/s
Total = 360MByte/s

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5. Registers
Register

Address

AccessFrameSynchronization

0x21F03C

R/W

Description
Selects the camera frame synchronization mode.
[0]: [Off]: Internal Synchronous mode[1]: [Bus]: Bus Synchronous mode

Table 1. Frame Synchronization Mode Register

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