MAXREFDES62# 系统板 放大+

概述

工业4.0¹标志着第四次工业革命，其特点是分布式、智能化控制系统。工业4.0摆脱了过去体积笨重、集中式的可编程逻辑控制器，允许工厂高度可配置、高度模块化，支持的传感器输入数量大幅增加，输出较之前更高。超小尺寸PLC，或称之为微型PLC，是工业4.0工厂的核心，以极小尺寸封装提供高性能，功耗极低。MAXREFDES62#是Maxim的微型PLC RS-485通信卡。

MAXREFDES62#具有两个RS-485收发器(一个为全双工，一个为半双工)，电源和数据隔离。每路驱动器输出具有可选择的120Ω端接电阻。MAXREFDES62#设计集成一个半双工RS-485收发器(MAX14783E)、一个全双工RS-485收发器(MAX14789E)、600VRMS数据隔离器(MAX14850)、STM32F1微控制器、FTDI USB-UART桥，以及隔离/稳压+3.3V电源轨(MAX17498C/MAX17515)。整个系统的功耗通常小于500mW，适合于信用卡大小的空间。用于工业和微型PLC领域时，MAXREFDES62#可用于任何要求RS-485高数据率和ESD保护的应用。方框图如图1所示。

图1. MAXREFDES62#参考设计方框图。

Detailed Description of Hardware

The power requirement is shown in Table 1.

Table 1. Power Requirement for the MAXREFDES62# Reference Design

Power Type	Input Voltage (V)	Input Current (mA, typ)
On-board isolated power	24	20

Note: STM32F1 and FTDI are powered by USB separately.

The MAXREFDES62# uses the ultra-efficient MAX17498C (U101) to generate the isolated +3.3V that powers the RS-485 transceivers from a 24V supply. This circuit is designed to maintain at least 3.0V of isolated power if one of the RS-485 drivers becomes shorted.

The MAX14850 (U300) digital data isolator provides data isolation between the SMT32F1 microcontroller and the MAX14783E and MAX14789E transceivers. The combined power and data isolation achieved is 600V_RMS.

The MAXREFDES62# uses the ultra-efficient MAX17498C (U501) to generate the isolated +17.5V, +7.5V, and -5V rails from a 24V supply. The MAX8719 (U102), MAX1659 (U103), and MAX1735 (U104) provide post-regulated +15V, +5.5V, and -3V rails. The MAX14850 (U301) digital data isolators provide data isolation. The combined power and data isolation achieved is 600V_RMS.

The MAX17515 (U100) step-down DC-DC converter converts the +5V supply from the USB to +3.3V and powers the STMicroelectronics STM32F1 (U200) microcontroller and FTDI (U400) USB-UART bridge.

Detailed Description of Firmware

The MAXREFDES62# uses the on-board STM32F103 microcontroller to communicate with the RS-485 transceivers. The user transmits and receives data through the RS-485 transceivers using a terminal program. The simple process flow is shown in Figure 2. The firmware is written in C using the Keil^® µVision5^® tool.

Figure 2. The MAXREFDES62# firmware flowchart.

The firmware accepts commands and transmits characters or text files through the MAX14783E. Connected in loopback, the transmitted data is received through the MAX14789E and compared to the original data that was sent. The complete source code is provided to speed up customer development. Code documentation can be found in the corresponding firmware platform files.

Quick Start

Required equipment:

• Windows^® PC with a USB port
• MAXREFDES62# board
• 24V power supply

Procedure

The reference design is fully assembled and tested. Verify board operation using the following steps:

Always disconnect and reconnect the USB cable before using the terminal program.

1. Turn or keep off the 24V power supply.
2. The MAXREFDES62# utilizes the FTDI USB-UART bridge IC. If Windows cannot automatically install the driver for the FTDI USB-UART bridge IC, the driver is available for download from www.ftdichip.com/Drivers/D2XX.htm.
3. Connect the negative terminal of the 24V power supply to the PGND (TP201) connector on the MAXREFDES62# board. Connect the positive terminal of the 24V power supply to the +24V (TP200) connector on the MAXREFDES62# board.
4. Turn on the 24V power supply.
5. Connect the USB cable from the PC to the MAXREFDES62# board.
6. Open the hyperterminal or a similar terminal program on the PC. Find the appropriate COM port, usually a higher number port, such as COM4 or COM6, and configure the connection for 921600, n, 8, 1, none (flow control). The MAXREFDES62# software displays a menu (Figure 3).
7. For immediate signal testing, configure the RS-485 transceivers in loopback mode as follows: Use a wire to connect the A terminal of the P300 terminal bock to the A terminal of the P301 terminal block. Use a wire to connect the B terminal of the P300 block to the B terminal of the P301 terminal block.
8. Press 0 in the terminal program to start the keypress loopback test.
9. Enter a character.
10. Verify that the character received is the same as the character sent.

Figure 3. Terminal program main menu.

Lab Measurements

Equipment used:

• Windows PC
• Oscilloscope
• MAXREFDES62# board
• +24V power supply

Figure 4. Loopback functionality (text file transfer), cable = 0m, termination enabled on both transceivers (CH1 = A, CH4 = B, MATH = A-B, CH2 = V_ISO).

Figure 5. Loopback functionality (text file transfer), cable = 30m, Cat5e, termination enabled on both transceivers (CH1 = A, CH4 = B, MATH = A-B, CH2 = V_ISO).

Reference

1. The new generation of manufacturing production is called Industry 4.0 in Germany and Smart Manufacturing System elsewhere. See, Securing the future of German manufacturing industry, Recommendations for implementing the strategic initiative INDUSTRIE 4.0, Final report of the Industrie 4.0 Working Group, Industry 4.0 Working Group, Acatech National Academy of Science and Engineering, April 2013, www.acatech.de/fileadmin/user_upload/Baumstruktur_nach_Website/Acatech/root/de/Material_fuer_Sonderseiten/Industrie_4.0/Final_report__Industrie_4.0_accessible.pdf. Henceforth cited as Industrie 4.0. Although the Industrie 4.0 report is focused on Germany, the implications of the German research and findings are recognized for industry in other countries. See also Ferber, Stefan, “Industry 4.0 – Germany takes the first steps toward the next industrial revolution,” Bosch Software Group, Blogging the Internet of Things, October 16, 2013, http://blog.bosch-si.com/industry-4-0-germany-takes-first-steps-toward-the-next-industrial-revolution/.
   
   There are many sources for Smart Manufacturing Leadership. An interesting summary report of issues and topics can be found at the Smart Manufacturing Leadership Coalition Committee Working Meeting, Minneapolis, MN, U.S., Thursday, October 20, 2011, https://smart-process-manufacturing.ucla.edu/workshops/2011-workshop/presentations/SMLC%2010-20-11v3.pdf. Also see, Implementing 21st Century Smart Manufacturing, Workshop Summary Report, Smart Manufacturing Leadership Coalition, June 24, 2011, https://smart-process-manufacturing.ucla.edu/about/news/Smart%20Manufacturing%206_24_11.pdf. A simple web search on the topic will reveal considerably more references.

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Keil is a registered trademark and registered service mark of ARM Limited.
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