MAXREFDES62#
MAXREFDES62# Datasheet
MAXREFDES62# RS-485 COMMUNICATIONS MICRO PLC CARD
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MAXREFDES62# |
MAXREFDES62# (pdf) |
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| System Board 5984 MAXREFDES62# RS-485 COMMUNICATIONS MICRO PLC CARD DETAILS MAXREFDES62# System Board Page 1 of 8 Enlarge+ Introduction The MAXREFDES62# features two RS-485 transceivers one full duplex and one half duplex with isolated power and data. Each driver output has a selectable termination resistor. The MAXREFDES62# design integrates one half-duplex RS-485 transceiver MAX14783E one full-duplex RS-485 transceiver MAX14789E 600VRMS data isolation MAX14850 a STM32F1 microcontroller a FTDI USB-UART bridge and isolated/regulated +3.3V power rails MAX17498C/MAX17515 . The entire system typically operates at less than 500mW and fits into a space roughly the size of a credit card. While targeted for industrial and micro PLC applications, the MAXREFDES62# can be used in any application that requires high RS-485 data rates and ESD protection. A block diagram is shown in Figure Page 2 of 8 Figure The MAXREFDES62# reference design block diagram. • High-speed RS-485 communication • Isolated power and data • Micro PLC form factor • Extended Protection with TVS on RS-485 Lines • Device drivers • Example C source code • Test data • Industrial control and automation • Process control • PLC Detailed Description of Hardware The power requirement is shown in Table Power Requirement for the MAXREFDES62# Reference Design Power Type On-board isolated power Input Voltage V Input Current mA, typ 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 600VRMS. 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 postregulated +15V, +5.5V, and -3V rails. The MAX14850 U301 digital data isolators provide data isolation. The combined power and data isolation achieved is 600VRMS. 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 The firmware is written in C using the tool. Page 3 of 8 Page 4 of 8 Figure 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 • 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. Turn or keep off the 24V power supply. 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 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. Turn on the 24V power supply. Connect the USB cable from the PC to the MAXREFDES62# board. 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 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. Press 0 in the terminal program to start the keypress loopback test. Enter a character. Verify that the character received is the same as the character sent. Page 5 of 8 Figure Terminal program main menu. Lab Measurements Equipment used: • Windows PC • Oscilloscope • MAXREFDES62# board • +24V power supply Page 6 of 8 Figure Loopback functionality text file transfer , cable = 0m, termination enabled on both transceivers CH1 = A, CH4 = B, MATH = A-B, CH2 = VISO . |
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