Digi BL1800 Battery Backup Circuit, Figure C-5shows the Jackrabbit battery backup circuitry

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C.2.1 Battery Backup Circuit

Figure C-5shows the Jackrabbit battery backup circuitry.

 

 

R12

VRAM

 

 

 

 

 

0 W

 

 

 

MMBT5088LT1

 

 

 

Q1

 

 

VBAT

 

R10

 

 

4.3 MW

 

R13

R14

3 V

 

 

 

 

 

1.3 kW

R15

 

 

 

 

 

 

D80

R80

 

 

0 W

 

 

 

 

 

D81

R81

 

 

0 W

 

 

 

 

 

D82

R82

 

 

0 W

 

 

 

Figure C-5. Jackrabbit Battery Backup Circuit

Resistor R12, shown in Figure C-5,is typically not stuffed on the Jackrabbit board. VRAM and Vcc are equal when power is supplied to the Jackrabbit. R13 prevents any cat- astrophic failure of Q1 from allowing unlimited current to enter the soldered-in battery.

Resistors R14 and R15 make up a voltage divider between the battery voltage and the tem- perature-compensation voltage at the anode of diode D80. This voltage divider biases the base of Q1 to about 2.6 V. VBE on Q1 is about 0.55 V. Therefore, VRAM is about 2.05 V.

These voltages vary with temperature. VRAM varies the least because temperature-com- pensation diodes D80–D82 will offset the variation with temperature of Q1 VBE. R80–

R82 may be stuffed instead of the corresponding D80–D82 to provide the optimum tem- perature compensation.

Resistor R10 provides a minimum load to the regulator circuit.

User’s Manual

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Contents Programmable Single-Board Computer Jackrabbit BL1800Digi International Inc TrademarksTable of Contents Index Schematics Introduction FeaturesDevelopment and Evaluation Tools Jackrabbit FeaturesHow to Use This Manual Additional Product InformationOnline Documentation CE Compliance ImmunityEmissions Safety Design Guidelines GeneralInterfacing the Jackrabbit to Other Devices Jackrabbit BL1800 Getting Started Development Kit ContentsDevelopment Hardware Connections Attach Jackrabbit to Prototyping Board BoardAssemble AC Adapter Connect Programming CableConnect Power Installing Dynamic C Run a Sample Program TroubleshootingWhere Do I Go From Here? Real-Time ClockTechnical Support BL1800 SubsystemsHeaders Jackrabbit PinoutsDigital Inputs Digital Inputs/OutputsHV3 Sourcing Output Digital OutputsConfigurable High-Current Output Changing HV3 to a Sinking Output Bidirectional I/OA/D Converter Schematic Diagram of A/D ConverterJackrabbit BL1800 D/A Converters Schematic Diagram of D/A Converters1 DA1 V ⋅ 1 e RCTypical DA1 Voltages for Various Duty Cycles Typical DA0 Voltages for Various Duty Cycles 2 DA0User’s Manual Serial Communication 1 RS-2322 RS-485 Ground recommended 485 R16 Programming PortUser’s Manual Programming Cable Changing Between Program Mode and Run ModeMemory SramFlash Eprom Other Hardware External InterruptsClock Doubler Spectrum Spreader Jackrabbit BL1800 An Overview of Dynamic C Software ReferenceJackrabbit BL1800 Jackrabbit Sample Programs Sample ProgramsSample Program DEMOJR1.C DEMOJR1.CWatch Expression Break Point Single-SteppingSummary of Features Editing the ProgramWatching Variables Dynamically 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 1 I/O Drivers Jackrabbit Function CallsVoid digOutint channel, int value Void anaOutint channel, int value Void anaInint channel, int *value Serial Communication Drivers Upgrading Dynamic C Patches and Bug FixesAdd-On Modules Appendix A. Specifications Figure A-1shows the mechanical dimensions for the Jackrabbit Electrical and Mechanical SpecificationsTable A-1. Jackrabbit Board Specifications Exclusion Zones Exclusion ZoneFigure A-3. User Board Footprint for Jackrabbit Figure A-4. Location of Jackrabbit Configurable Positions Jumper ConfigurationsTable A-2. Jackrabbit Jumper Configurations Conformally coated area Conformal CoatingJackrabbit Use of Rabbit 2000 Parallel PortsTable A-3. Jackrabbit Pinout Configurations PD0 PD1 Jackrabbit BL1800 Appendix B. Prototyping Board Prototyping Board Overview Jackrabbit Connectors User LEDs BuzzerPrototyping Board Features Top Side Mechanical Dimensions and LayoutTop Side Using the Prototyping BoardRelay Demonstration BoardExisting Top Side Prototyping BoardPE0 VCC HV0 SM1 SM0 HV2 Stat Jackrabbit BL1800 Power Supplies Appendix C. Power ManagementDcin Current mA 950 mA·h = 5.4 years 20 µA Batteries and External Battery ConnectionsFigure C-5shows the Jackrabbit battery backup circuitry Battery Backup CircuitReset Generator Power to Vram SwitchChip Select Circuit Figure C-7shows a schematic of the chip select circuitJackrabbit BL1800 SMODE0 SMODE1 IndexRABDB01.C RABDB02.C Schematics