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MOTG-RS485

Description

MOTG-RS485

RS485 is a standard communication port for various industries and networking equipment and enables easy configuration of local networks and multipoint communications links. Unfortunately, most of the microcontrollers do not support RS485 voltage levels.

MOTG-RS485 provides a high-speed and low-cost solution for incorporating RS485 Serial communication into your design.

Features

  • ST1480ACDR differential line transceiver
  • 3.3V power supply only
  • ESD protection: ±15 kV human body model
  • Guaranteed 12 Mbps data rate
  • 7 to 12 common model input voltage range
  • Supports 2-wire 3.3V/5V TTL UART interface

Before Getting Started

Out of the box, the chipset's UART pins are not connected to the UMI of the MOTG.

MOTG-RS485 hardware allows the UART pins to be connected to either TX, RX or GPIO1, GPIO2 of the UMI. This is could be achieved by shorting the respective sides of solder bridges SB2 and SB3 using a solder blob and a soldering iron. This is done by the User.

MOTG

Unless the designer intends to use two UART MOTGs on a gen4-MOTG-AC2 or gen4-MOTG-AC4 board, the UART pins should be directed to TX, RX of the UMI as shown above.

When two UART MOTGs are being used on a gen4-MOTG-AC2 or gen4-MOTG-AC4 board, the UART pins of one of the MOTGs should be diverted to GPIO1 and GPIO2 of the UMI, as shown below. This prevents both MOTGs from using the same pins of the gen4 display module for UART communication.

UART MOTGs

Chipset Features

MOTG-RS485 carries a ST1480ACDR differential line transceiver. The datasheet for the ST3232 is available from the https://www.st.com/ website.

Pins and Solder Bridges

Pin Description

Pin Description

Pin Symbol Description
1 3.3V 3.3V Input Supply
2 GND Supply Ground
3 RX Asynchronous Serial Receive Pin
4 TX Asynchronous Serial Transmit Pin
5 GPIO5 Turn Around Pin, DE/RE
6 N/C Not Connected
7 N/C Not Connected
8 GPIO2 RX Bypass Pin
9 GPIO1 TX Bypass Pin
10 N/C Not Connected
11 N/C Not Connected
12 N/C Not Connected
13 N/C Not Connected
14 N/C Not Connected
15 GND Supply Ground
16 N/C Not Connected

Note

The designer can choose if the UART pins of the MOTG should be connected to either TX, RX or GPIO1, GPIO2 of the UMI. This could be achieved by shorting the respective sides of solder bridges SB2 and SB3. This is discussed in detail in Before Getting Started.

Please take note that the GPIO5 marking is missing on the PCB silkscreen overlay on PCB HW REV 1.1. This is the Turn Around pin and is used to select if the module is transmitting or receiving. Please refer to the schematic to see the connection details.

Solder Bridge Description

The MOTG-RS485 also has three solder bridges. The functionality of those solder bridges is described in the table below. These are soldered by the User.

Solder Bridge Description

Solder Bridge Description
SB1 Use terminating resistor
SB2 TX selector
SB3 RX selector

Note

Each differential pair of wires is a remission line and proper termination of the line will prevent reflection. MOTG-RS485 has a termination resistor (120 ohms) for this purpose. Solder Bridge 1 (SB1) provides the option for using the terminating resistor in the module.

Mechanical Views

Mechanical Views

Note

PCB Silkscreen on REV 1.1 PCBs is missing the GPIO5 label.

Schematic Details

Specifications

Recommended Operating Conditions

Parameter Conditions Min Typ Max Units
Supply Voltage (VCC) 3.0 -- 3.6 V
Operating Temperature 0.0 -- 70.0 °C
Input Low Voltage (VIL) DE, DI, RE -- -- 0.8 V
Input High Voltage (VIH) DE, DI, RE 2.0 -- -- V

Global Characteristics Based on Operating Conditions

Parameter Conditions Min Typ Max Units
Supply Current (ICC) No Load, DI = 0 V or VCC, DE=VCC, RE=0 V or VCC -- 1.3 2.2 mA
Transmitter Input Voltage No Load, DI=0 V or VCC, DE=0 V, RE=0 V -- 1.2 1.9 mA
Control Input Voltage -0.3 -- 7.0 V
Driver Input Voltage -0.3 -- 7.0 V
Receiver Output Voltage -0.3 -- VCC+0.3 V
Receiver Input Voltage -14.0 -- 14.0 V
Driver Output Voltage -14.0 -- 14.0 V

Revision History

Hardware Revision

Revision Number Date Description
1.1 21/11/2016 Initial Public Release version

Datasheet Revision

Revision Number Date Description
1.8 06/01/2023 Modified datasheet for web-based documentation