Digi BL1800 user manual Serial Communication, 1 RS-232, 2 RS-485

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3.5 Serial Communication

The Jackrabbit has two RS-232 (3-wire) serial channels, one RS-485 serial channel, and one synchronous CMOS serial channel.

3.5.1 RS-232

The Jackrabbit’s two RS-232 serial channels are connected to an RS-232 transceiver, U4, an industry-standard MAX232 chip. U4 provides the voltage output, slew rate, and input voltage immunity required to meet the RS-232 serial communication protocol. Basically, the chip translates the Rabbit 2000’s 0 V to +Vcc signals to ±10 V. Note that the polarity is reversed in an RS-232 circuit so that +5 V is output as –10 V and 0 V is output as +10 V. U4 also provides the proper line loading for reliable communication.

The Rabbit 2000 serial port B signals are presented as RS-232 compliant signals TXB (serial port B transmit) and RXB (serial port B receive) on header J5.

The Rabbit 2000 serial port C signals are presented as RS-232 compliant signals TXC (serial port C transmit) and RXC (serial port C receive) on header J5.

The maximum baud rate for each RS-232 serial channel is 115,200 bps. RS-232 can be used effectively at this baud rate for distances up to 15 m.

Because two RS-232 transmit and two RS-232 receive lines are available, one serial chan- nel can be used for serial transmit and receive, and the other serial channel can be used as a general digital I/O for RTS/CTS handshaking. Although the present release of Dynamic C does not support RTS/CTS handshaking in its libraries, it is possible to write your own software.

3.5.2 RS-485

The Jackrabbit has one RS-485 serial channel, which is connected to the Rabbit 2000 serial port D through U6, an RS-485 transceiver. U6 supports the RS-485 serial communica- tion protocol. The chip’s slew rate limiters provide for a maximum baud rate of 250,000 bps. The half-duplex communication uses the Rabbit 2000’s PD5 pin to control the data enable on the communication line.

The Jackrabbit can be used in an RS-485 multidrop network. Connect the RS-485+ to RS-485+ and RS-485– to RS-485– using single twisted-pair wires (nonstranded, tinned) as shown in Figure 11.

28	Jackrabbit (BL1800)

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Contents Jackrabbit BL1800 Programmable Single-Board ComputerTrademarks Digi International IncTable of Contents Index Schematics Features IntroductionJackrabbit Features Development and Evaluation ToolsOnline Documentation How to Use This ManualAdditional Product Information Emissions CE ComplianceImmunity Interfacing the Jackrabbit to Other Devices SafetyDesign Guidelines General Jackrabbit BL1800 Development Kit Contents Getting StartedDevelopment Hardware Connections Board Attach Jackrabbit to Prototyping BoardConnect Programming Cable Assemble AC AdapterConnect Power Installing Dynamic C Troubleshooting Run a Sample ProgramTechnical Support Where Do I Go From Here?Real-Time Clock Subsystems BL1800Jackrabbit Pinouts HeadersDigital Inputs/Outputs Digital InputsDigital Outputs HV3 Sourcing OutputConfigurable High-Current Output Bidirectional I/O Changing HV3 to a Sinking OutputSchematic Diagram of A/D Converter A/D ConverterJackrabbit BL1800 Schematic Diagram of D/A Converters D/A ConvertersV ⋅ 1 e RC 1 DA1Typical DA1 Voltages for Various Duty Cycles 2 DA0 Typical DA0 Voltages for Various Duty CyclesUser’s Manual 2 RS-485 Serial Communication1 RS-232 Ground recommended Programming Port 485 R16User’s Manual Changing Between Program Mode and Run Mode Programming CableFlash Eprom MemorySram Clock Doubler Other HardwareExternal Interrupts Spectrum Spreader Jackrabbit BL1800 Software Reference An Overview of Dynamic CJackrabbit BL1800 Sample Programs Jackrabbit Sample ProgramsDEMOJR1.C Sample Program DEMOJR1.CSingle-Stepping Watch Expression Break PointWatching Variables Dynamically Summary of FeaturesEditing the Program User’s Manual Other Sample Programs Illustrating Digital I/O R/W pin and DB0-DB3 on 3 RS-232 Serial Communication Sample Programs 4 RS-485 Serial Communication Sample Program Cooperative Multitasking Int vswitch Advantages of Cooperative Multitasking Jackrabbit Function Calls 1 I/O DriversVoid digOutint channel, int value Void anaOutint channel, int value Void anaInint channel, int *value Serial Communication Drivers Add-On Modules Upgrading Dynamic CPatches and Bug Fixes Appendix A. Specifications Electrical and Mechanical Specifications Figure A-1shows the mechanical dimensions for the JackrabbitTable A-1. Jackrabbit Board Specifications Exclusion Zone Exclusion ZonesFigure A-3. User Board Footprint for Jackrabbit Jumper Configurations Figure A-4. Location of Jackrabbit Configurable PositionsTable A-2. Jackrabbit Jumper Configurations Conformal Coating Conformally coated areaUse of Rabbit 2000 Parallel Ports JackrabbitTable A-3. Jackrabbit Pinout Configurations PD0 PD1 Jackrabbit BL1800 Appendix B. Prototyping Board Jackrabbit Connectors User LEDs Buzzer Prototyping Board OverviewPrototyping Board Features Mechanical Dimensions and Layout Top SideUsing the Prototyping Board Top SideDemonstration Board RelayExisting Prototyping Board Top SidePE0 VCC HV0 SM1 SM0 HV2 Stat Jackrabbit BL1800 Appendix C. Power Management Power SuppliesDcin Current mA Batteries and External Battery Connections 950 mA·h = 5.4 years 20 µABattery Backup Circuit Figure C-5shows the Jackrabbit battery backup circuitryPower to Vram Switch Reset GeneratorFigure C-7shows a schematic of the chip select circuit Chip Select CircuitJackrabbit BL1800 Index SMODE0 SMODE1RABDB01.C RABDB02.C Schematics