The hottest industrial features are crucial in emb

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Industrial characteristics are crucial in embedded processing

many general-purpose signal processors have good computing performance and basic connection characteristics, so they can be accepted by industrial applications. On the other hand, some important peripheral enhancements can significantly improve the capability of the processor and make it suitable for industrial systems with higher requirements. This paper will discuss two examples of enhanced functions in the application of network and motor control

Ethernet interface

for traditional industrial applications, Ethernet controller can provide basic network connection. The controller (MAC) and processor are usually located on the same chip. It is generally used with an external PHY chip to form a complete interface

external mac/phy chips can also be used, which are often directly connected to the asynchronous memory interface of the processor. Although the price of Ethernet mac/phy integrated chips continues to decline, and has reached a level almost equivalent to that of independent PHY chips, its transmission rate cannot be compared with that of integrated MAC plus external PHY solutions. This is because the internal MAC is usually connected to the system DMA channel and can be set to send or receive data, with little interaction with the kernel processor. The internal MAC controller can generally achieve performance close to the line speed, depending on the protocol

Another important aspect of performance is the processor load required to achieve a given throughput rate. This is part of the overall performance and the biggest difference between internal MAC solutions and external MAC solutions

in industrial networks, Ethernet can use network time protocol (NTP) to provide basic system time. For NTP based systems, the synchronization of the entire controlled network is measured by the "man-machine interface" time scale. Although the protocol is suitable for general systems, many groups of experimental information are required in the general experimental requirements, it is not accurate enough and is not suitable for many industrial control systems that require more precise synchronization

in order to improve accuracy, the industry has formulated IEEE 1588 precision time protocol (PTP) standard, which is used in conjunction with Ethernet controller and network stack to synchronize the "local" clock on the network by using the master clock. That is, each processing or control node is synchronized with the main reference time of the drive system

by keeping the precise timing relationship of the entire industrial network, time events can be synchronized to the sub millisecond level. Time events include when the analog/digital converter samples, when the digital/analog converter is driven, and when the i/o line is activated to perform system control

ieee 1588 PTP requires the exchange of specific packets to provide time information from two nodes. These packets are used to calculate the time and frequency difference between the clocks of each node. In addition, the protocol provides a way to continuously adjust the clock to keep each clock synchronized

ieee1 some units charge indiscriminately with the help of administrative power and influence; 1 some fields lack market competition 1588 PTP protocol can be realized completely by software or by the combination of hardware and software. Hardware based solutions provide the best accuracy, so the best synchronization can be achieved between nodes. When adopting the hardware solution, the timestamp of the data packet can be as close as possible to the interaction point between it and PHY. In this way, the jitter between nodes is lower

pwm unit

a standard peripheral of microprocessor and DSP is general timer, which provides standard timer function based on one or more clock references inside or outside the chip. On the pin interface, it can also provide width capture or pulse counting functions, as well as single ended pulse width modulation (PWM) output waveform. These PWM outputs usually have programmable pulse width and period, and can be used in many task control applications, including DC level generation and anti noise analog signal transmission (using appropriate low-pass filtering)

however, in order to make it really be used in AC motor control, the basic PWM function needs to be upgraded from several aspects. Figure 1 shows the schematic block diagram of motor control, in which the PWM output from the processor drives the high-end and low-end power supply devices in a differential manner, so as to adjust the torque and speed of the motor. ADC is used to provide current measurement feedback to the processor, so that PWM duty cycle can be managed in a closed-loop system with tight timing in order to control the motor

Figure 1: schematic diagram of motor control signal chain

compared with the PWM module of general processor, the PWM unit for motor control has many enhanced functions. As mentioned above, the motor control PWM is used in pairs to alternately drive the high-end and low-end power switches at a given motor phase. For three-phase AC motors, three pairs of PWM units are required

as shown in Figure 1, isolation must generally be provided between the PWM control unit of the processor and the gate driver of the power transistor. This isolation is usually achieved by optical couplers or pulse transformers. Therefore, some PWM units provide grid driving units to facilitate the mixing of output and high-frequency chopper signals, so as to connect to the pulse transformer; At the same time, it is also equipped with a pin driver to drive most optocouplers with sufficient source current and suction current

importantly, motor control PW innovation countries encourage the development of major environmental protection technology, and the implementation and utilization methods and channels of equipment m must provide a certain guarantee "dead zone" between the end of one power supply device declaration and the beginning of another complementary power supply device declaration. Otherwise, the power switch may have a DC short circuit

in addition, there must always be a way to immediately disable PWM output asynchronously, so as to avoid the error condition that multiple output phases are started at the same time. This "PWM jump" feature allows the use of an external asynchronous signal to disable all PWM outputs, regardless of the state of the processor clock

finally, although it is a common practice to start the general timer synchronously, PWM timer synchronization is of more significance for motor control. The "PWM synchronization" signal applied internally or externally can be used to generate an interrupt (sometimes more than once per cycle), so that the processor can adjust the duty cycle according to the control algorithm, and ADC can obtain and transmit the current measurement results with strong comparability of the next mechanical performance testing machine

at this point, it is obvious that although many task industry applications may choose processors with general peripheral sets, it is wise to first consider which "industrial upgrades" are beneficial to current applications. In this paper, we only choose to discuss two examples of network connection and PWM function, but the same principle also applies to many other subsystems, including memory structure and data conversion interface. The stability and system control ability of industrial products can be improved by using the value-added brought by expanding peripherals and system modules. (end)

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