51 Research and Design, Electronic Engineers website - Embedded Systems, MCU, DSP, EDA, Test and Measurement, Components, Communications, Power, Microelectronics, Semiconductors

    Abstract: Monolithic integrated circuit (micro controller, MCU) the connectivity is becoming the belt or a many network interface MCU additional standard. This article introduced that the country gives extra or a many network interface MCU development, the network constitution, the chip select, the embedded wireless network and the application situation.

    Key word: MCU network network interface embedded system network embedded wireless network

The micro controller no longer works in the isolation condition, from the factory floor to the automobile, everywhere has the distribution computation presence. The belt double ethernet or CAN (control local area network) bus interface MCU are very useful, but this is also only a tip of the iceberg.

Now, has each form and the size network. Many embedded systems had many kinds of networks. Along with TCA (telecommunication computation construction) new progress, its switch structure network (switch-fabric network) remarkable. It may be the ethernet, used for I2C (interior integrated circuit) the main line to support IPM (synthesis power management) the controller (IPMC), this was an construction management support part.

Today, although obtains the correspondence software to be quite complex, but chooses one kind with network matching MCU is quite easy. Uses the district in the multiple joint either the multi-networks (or piecemeal) applies, may solve the durable aspect problem. Compares with the distributed processor, the networking can also reduce the electric cable demand, and allows the system to be composed of the inexpensive MCU array, thus replaces a pair of high performance the processor.

    The MCU network has covered the widespread embedded environment. The ethernet is the most popular network, specially to the Internet and local area network’s connection. The RS-232 connection is very popular, but its speed is slow, mainly uses for the installment which controls; But applies in the network gateway, is higher to the connection request. To many embedded design questions. The research and development may choose or many appropriate network interfaces solve.

1 network and peripheral device

The popular network interface is installs on MCU (see Table 1 and Table 2 rows). The serial interface is very popular, it mainly uses in the serial interface equipment, but does not support the network. Some connections carry out SLIP (serial link connection agreement) or PPP (point to point protocol), (MODEM) connects through the modem with the Internet.

Table 1 connects the main line to use in the MCU network situation

Table 2 network interfaces

The ethernet is the present is most general, on its high speed hardware very easy insertion piece system (SoC). In order to connects many kinds of equipment and the Internet, increases the ethernet already becomes very important.

Afterward, USB (universal serial bus) more appeared in MCU. At first, is regards MCU a USB peripheral device to process. Supports USB the main engine to be always useful, MCU serves as the keyboard to have equally likely the PC style equipment, moreover works together with the storage device and other USB peripheral device well. USB in these approach in main engine’s exterior embedded network become more important.

Is inserting MCU the connection to have 1394 (high speed bus interface) slowly. This kind of situation possibly changes along with the 1394b appearance, it stressed that is takes the multimedia networks the infrastructures.

The CAN main line is one kind of network interface, its popular procedure and the ethernet are the same, when after particularly it enters the automobile and the process control environment, was this.

2 equipment networks

What MCU is more general is with CAN, LIN (partial interconnecting network), SPI (serial peripheral device connection), I2C and the single track (1Wire) the main line connects. Although these connection’s running rate is slower than the ethernet, but they easier to realize. Some equipment’s host installment, looks like the single track agreement, can use the software to realize completely, but the ethernet very little has the equipment which can do this.

CAN already has found own position in the automobile and in the process control industry. It receives the widespread support, and suits the embedded application scope, commonly used in LIN hierarchic network.

The speed is 20kb/s LIN suits the low performance network. What although aims is the automobile industry, but LIN may take the sensor, enters other embedded application network conveniently. CAN and LIN have the merit which the single track designs. As the majority single track designs, adopts to the equipment altogether is effective.

The national semiconductor and Motorola Corporation have developed SPI, it uses main/from the construction way, with from machine the data collection, the reorganization system link in together (daisy-chain together), if the strength shows. Must realize the serial peripheral device connection is quite simple, to maintain approaches main engine’s SPI from machine, uses the independent chip select.

The I2C use double thread clock main line, supports main/from and the multi-constructions. From advanced TCA to battery’s surveillance. I2C has found own position in the widespread embedded application scope. A movement under 3.4Mb/s high speed can the edition work when the 100kb/s scope also same good. Phillips is one of I2C supporters.

The I2C synchronized characteristic and each byte’s confirmation (per-byteacknowledgement), enables it to realize quite easily with the hardware. If does not have the massive software overhead, it to UART (general asynchronous transceiver) the execution does not have the help. With the ethernet, CAN and the LIN comparison, I2C have the widespread retail merchant support.

The single track construction is the host who special-purpose has a segment/from the network. Who can the main network pipe union develop, but must register from the network. Has each kind of informed sources (source) to provide to the single track from the equipment. This construction to simple, the low power loss equipment is very useful.

On MCU, the independent network interface has succeeded period of time. Afterward, what appears is more than a connection MCU. This allows MCU to make the gateway which between the network connects.

3 gateway chips

Has pair of network interface MCU, in network processor (it can support 6 kind of networks) from Ubicom Corporation’s low price IP3023 to NEC Corporation’s 400MHz, 64 Vr7701 processor (it to have a pair of 10/100Mb/s ethernet connection) on to be able to move. These MCU can with ease support the resident gateway and the set-top box application. Many MCU retail merchants are impelling in this scope application solution. Ethernet’s gateway maintained at SOHO (small work and family work) the environment unpopularity. With the aid in shipping (shipment), elects Can the CAN gateway actually collar in the ethernet, this is because it located at majority automobiles.

The bridge application constituted another domain, has applied in there MCU in the entertainment, plays and performs. In these applications, different network connections in together. Can the LIN bridge, for instance the Mitsubishi Electron Company’s M16C product, used in the automobile environment. In this environment, possibly must support many bridges to isolate the automobile electronic installation’s different part. Can turn on inexpensive LIN Can the LIN bridge to carry on the deposit from the processor. Although CAN is the quite cheap network, but the LIN equipment is cheaper. The two have used the single track connection, causes the key choice factor the cost becomes low, as shown in Figure 2.

Today, arrives at SPI the ethernet to I2C and the ethernet, in fact is completes under the computer system management. Similar, CAN equipment in process control environment popular. Several examples, have CAN 2.0b including Microchip Corporation’s PIC MCU and the Japanese date six company’s H8 products, and supports SPI or the I2C network. Even has the single equipment, looks like Lan-tronix Xport, it has used X186 (based on DSTNI LX) MCU, brings the built-in bridge joint serial device’s ethernet, the overall system interior installs the disposition to have the expansion RJ45 plug (i.e. crystal).

4 embedded wireless networks

Until now, the wireless network may be definitely popular, but the instance MCU popular wireless solution not yet appeared, like 802.11, blue teeth and ZigBee(802.15) all needs to have the massive hardware circuit block outside MCU. The support network protocol and the ethernet are the same rank, must integrate the agreement in the small network the difficulty to be more. ZigBee wants the conformity to MCU, looks like is easiest, because its working speed is slower, needs the power loss is lower, the agreement is simpler.

The resident gateway, these wireless gateways, are specially higher than in the embedded network to the safe request to the isolation request some. Why did this is look like IDT Corporation’s RC32365 chip conformity encryption hardware’s principle. In order to support VPN (Virtual Person Network, hypothesized individual network) designs MCU which provides, but also needs to include pair of ethernet MAC (media access control) and SPI.

Distributes embedded system’s solution, constitutes easily with such MCU, in these MCU conformity majority of (, if is not the hardware which complete words) or many networks need. Chooses the correct network is possibly a more difficult duty, but has the quite great scope to be possible at least the free choice, this is beneficial.

5 single track networks

The single track is Maxim Corporation integrates the product private network construction. Its benefit from the inexpensive host/from the construction, including on the small line which uses to the message center provides the low power the ability.

The single track main engine only uses the simple root I/O line on MCU, is very easy through the software to realize. Many MCU had the single track main engine route. The USB- single track and the serial - single track’s bridge chip also appeared.

The main engine has not registered the limit, the registration accompanies machine enters the movement, each from machine has an only 64 string of bit store. The initial handshake agreement permission main engine distinguishes each Taiwan alone from machine.

Automated information product manager Hal Kurkowski which works in Dell Semiconductor /Maxim Corporation pointed out: The single track method can give from the equipment power supply (as shown in Figure 3). When data transmission, on capacitor maintenance equipment’s voltage.

When necessary, the structure main engine has the possibility to provide a bigger power through the main line. In this situation, the main engine must be able to program, like this in the request delivers after the equipment, 22Ω the source resistance is cut alternately. Some based on dodges quickly the memory equipment’s example, programs to the memory when need more powers. This time the main engine will request to the equipment transmission that cuts into the power source, waited for stipulated time, then cuts returns to 1.2kΩ the resistance.