USB2.0 vs IEEE 1394

in recent years, with the popularization of multimedia devices and mobile data peripherals, the use of high-speed serial interfaces has become increasingly important. Currently, two peripheral interfaces are used on the computer: USB 1394 and IEEE. So what are the differences between the two parallel driving interfaces: USB 1394 and IEEE? What are their advantages?

I. USB specification
USB is the abbreviation of Universal Serial Bus. Its Chinese meaning is "Universal Serial Bus ". It is an interface technology applied in the PC field and is jointly developed by Intel,
NEC, Compaq, Dec, IBM, Microsoft, and Northern Telecom. However, USB is not a bus standard, but an input/output interface standard for connecting a computer system to a peripheral device . USB uses a 4-pin standard plug and chrysanthemum link to connect all peripherals. In theory, USB can be mounted to 127 devices. The hardware part of the USB system is generally composed of three parts: USB Host Controller/root hub, USB hub, and USB device.
tips: Each USB device uses 7-bit data for addressing. The value of 7 times is 128, minus the 00 address occupied by the host. A maximum of 127 devices are supported. Of course, 127 is only a theoretical value, but it is not necessarily possible. Currently, only 111 Peripherals can be connected.
currently, the USB specifications mainly include V1.1 and V2.0. In addition to the Mbps and 12 Mbps transmission modes specified in USB, USB also adds a Mbps high-speed data transmission mode (note: the second version of 800 will have a transmission rate of 1600 Mbps, with a maximum ideal value of Mbps ). Although the transmission speed of USB is greatly improved, the working principle and mode are exactly the same as those of USB, the most critical technology for to increase the transmission speed to 480 Mbps is to increase the unit transmission rate : the Unit data transmission time of USB1.1 is 1 Ms , the Unit data transmission time of USB2.0 is 125 microseconds .

at the same time, USB adopts a backward compatible design. In USB
, " enhanced Host Controller Interface" (EHCI) defines an architecture compatible with USB1.1, using a group of Communication Protocol extensions and new hardware components developed for connection ports: transfer translator . the buffer memory of the transfer interpreter, which can be accessed by a transmission device at full speed or at low speed, directly connect to the port for transmission . In this way, the USB driver Program can be used to drive the USB device for backward compatibility. However, the USB Hub does not directly use the 12mbps transmission rate as the USB hub. The data transmission process is as follows: that is, USB2.0 hub first identifies whether the inserted USB device is USB or USB. If you are using USB, convert
Mbps of USB to 12 Mbps of USB.
tips: The maximum transmission rate of USB2.0 is 480 Mbps, that is, 60 Mb/s. However,
This is a theoretical transfer value. If several devices share a USB channel, the master control chip allocates and controls the bandwidth available to each device. For example, in USB1.1, all devices can only share the bandwidth of
1.5 Mb/s. If a single device occupies all the bandwidth of the USB interface, it will bring difficulties to other devices. This is similar to Internet sharing.

Ii. IEEE 1394 specifications
In 1987, Apple launchedHigh-speed serial bus-Fire WireTo replace the parallel SCSI bus. Later, the IEEE alliance developed the IEEE 1394 standard (I. Link ).

IEEE 1394Chrysanthemum chain configuration.Tree Structure ConfigurationBut it still uses linear links to form various linear branches in the tree structure. The IEEE 1394 bus also requires a master adapter to be connected to the system bus. Generally, we name the primary adapter and its port as the primary port. The master port is the root node of the IEEE 1394 bus Tree Configuration Structure. A master port can connect up to 63 devices. These devices are called nodes. They can form a parent-child relationship (). The cables between two adjacent nodes are up to 4.5 m, however, when two nodes communicate with each other, a maximum of 15 nodes can be transferred in the middle.
Therefore, the maximum communication distance is 72 m, and the cable does not need a receiver.

Unlike USB, all resources in the IEEE 1394 standard interface structure are in the form of Unified Storage addressing, which is identified by storage transformation for resource configuration and management. Therefore, in this sense, IEEE 1394 can be considered as a bus system equivalent to PCI bus.
Structure. In addition, compared with USB, IEEE 1394 supports synchronous and asynchronous transmission. Asynchronous transmission is a traditional transmission method. when data is transmitted between the host and peripherals, data is not transmitted in real time.
The data is delivered to the host in batches, but the data accuracy is very high, which is the main feature. Synchronous Transmission emphasizes the real-time data. With this feature, devices can directly transmit data through
The IEEE 1394 high-bandwidth and synchronous transmission are directly transferred to the computer, reducing the previous expensive buffer devices. This is why IEEE 1394 has been used as the standard interface for digital cameras.
I.

Currently, IEEE 1394 only has two specifications. One is IEEE 1394a, which is currently the mainstream specification and mainly supports two modes.
─ Backplane mode and cable mode. The backplane mode only supports transmission rates of 12.5 Mbps, 25.5mbps, or 50 Mbps, while
The cable mode provides the required 100 Mbps, 400 Mbps, and Mbps. However, the transmission speed of IEEE 1394 follows the principle from low: because it is in the same network
The data in the network can be exchanged at different rates. However, if a Mbps device is added to two devices with a transmission rate of Mbps, the data transmission speed is
Mbps. The other is IEEE 1394b, which is the standard for the next generation PC. It will be extended directly from the Mbps of IEEE 1394a
1600 Mbps and 3.2 Mbps. If optical fiber is used, the maximum transmission rate is increased to Gbps. In addition, compared with IEEE 1394a, IEEE 1394b uses
The connection distance is 100 meters (note: this will reduce the transmission rate to 100 Mb/s at the cost of reducing the transmission rate) and provide power supply solutions for internal devices. In addition, the IEEE Alliance
The IEEE 1394b specification introduces a new physical layer configuration called "betamode" to improve the management capability of the IEEE 1394b system.

3. Whoever wins or loses
1. High Cost

In terms of cost, USB2.0 is dominant. Because the current Motherboard chipset has built-in USB master controller, and currently most peripherals are standard with USB interface. Therefore, you can enjoy the convenience of USB without having to invest any other fees. For IEEE 1394, the structure of the IEEE 1394 controller is complicated. To integrate the controller into the Motherboard chipset, either technically or cost-effectively, so there are very few chipset integrated with IEEE 1394 controller on the market. To implement the IEEE 1394 functionThe motherboard is provided in the form of an integrated additional chip. Generally, it can only be achieved by inserting an IEEE 1394 expansion card.In this way, the result is that the cost of use has increased.

2. ease of use
IEEE 1394 is dominant in terms of ease of use. Although both of these specifications support hot plugging, requires Windows XP SP1 to support the Operating System (note: although Windows 2000/XP supports USB, only USB 1.1 standards are supported. Therefore, the transmission rate of USB is greatly reduced, in
Windows or earlier versions, the driver must be installed ). From Windows 98 onwards, we have provided full support for IEEE 1394. The installation of
IEEE 1394 can be used without any driver, which is not comparable to that of USB. IEEE 1394 supports point-to-point functions . If two computers are connected, you do not need to set the IP address or settings for the computer. In addition, USB2.0 only provides 5 v dc voltage and 0.5a current , although it is enough for General devices, however, an external power supply is required for devices with high power consumption, such as external recorders, Mo drivers, and printers. IEEE 1394 provides 8 V ~ The voltage of 40 V and the current of 5a can theoretically provide up to
200 W (40 V × 5a) power, far higher than 1394 (a stronger power supply is required if such a high power is to be achieved, but such a high power supply is used only when many IEEE devices are connected in series. Who will use so many IEEE 1394 devices at once ?).

3. transmission speed
although USB2.0
can provide 480 Mbps, slightly higher than the 400 Mbps provided by IEEE 1394a, does it mean that USB2.0 is more advantageous? The answer is no. Generally,
the actual transmission speed of USB is only 2 ~ of USB ~ 13 times , far less than its theoretical value, and if several devices share a USB channel, the main control chip allocates and controls the bandwidth that each device can control, the transmission speed is lower. This is rare in the mainstream IEEE 1394a. From the test results (see
table), IEEE 1394a is far better than USB2.0 in terms of abrupt transmission rate, average read/write rate, workstation performance, and file copy speed ., we can imagine that the advantage of IEEE 1394b is more obvious. However, one disadvantage of IEEE 1394 is that the IEEE 1394 bus occupies a large amount of resources, so high-speed CPU is required to achieve the optimal transmission rate
.
it can be said that IEEE 1394 has advantages over USB in terms of performance and application. However, IEEE 1394 was first positioned for multimedia applications , unlike popular USB routes , therefore, IEEE 1394 devices are much more expensive than USB devices. In addition, IEEE 1394 is subject to a high patent fee, resulting in high usage costs . This is the biggest weakness of IEEE 1394. However, with the integration of the IEEE 1394 controller into the chipset in the future, we believe this problem will be mitigated. In addition, it is worth noting that IEEE 1394 adopts a non-master-slave architecture design mode, and peripheral devices can transmit data from point to point without using computers , this is incomparable to 1394, which is also the main space for
IEEE.
in the future, the IEEE 1394 and USB interfaces will be compatible.