Digi BL1800 user manual Schematic Diagram of D/A Converters

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3.4 D/A Converters

Two digital-to-analog (D/A) converter outputs, DA0 and DA1, are supplied on the Jack- rabbit. These are shown in Figure 10.

The D/A converters have no reference voltage. Although they may be fairly accurate from one programmed voltage to the next, they do not have absolute accuracy. This is because Vcc can change ±5%, the PWM outputs might not achieve the full 0 V and 5 V rail out of the processor, and the gain resistors in the circuit have a 1% tolerance. The D/A converters therefore need individual calibration, with the calibration constants held in software before absolute accuracy can be relied on. The Jackrabbit is sold without such calibration.

			Vcc
		R29
		1 MW
	DA0	R26
	DA0
	82.5 kW				R22
		–	2		R22		PD2
			2
	1				10 kW

		LM324	3			R21
	R20	+	3				PD1
	R20	+	R27		C20	110 kW	PD1
	1.1 kW		R27		C20	110 kW
	1.1 kW		255 kW	100 nF
	DA1	R28
	DA1
	100 kW
		–	6
		–
	7	LM324	5		R24
	R25	+	5				PD4
	R25	+	C22		100 kW		PD4
	1.1 kW		C22		100 kW
	1.1 kW		100 nF
			100 nF

Figure 10. Schematic Diagram of D/A Converters

Note that DA0 is used to provide a reference voltage for the A/D converter and is unavail- able for D/A conversion when the A/D converter is being used.

Pulse-width modulation (PWM) is used for the D/A conversion. This means that the digi- tal signal, which is either 0 V or 5 V, is a train of pulses. This means that if the signal is taken to be usually at 0 V (or ground), there will be 5 V pulses. The voltage will be 0 V for a given time, then jump to 5 V for a given time, then back to ground for a given time, then back to 5 V, and so on. A hardware filter in the circuit consisting of a resistor and capacitor averages the 5 V signal and the 0 V signal over time. Therefore, if the time that the signal is at 5 V is equal to the time the signal is 0 V, the duty cycle will be 50%, and the average signal will be 2.5 V. If the time at 5 V is only 25% of the time, then the average voltage will be 1.25 V. Thus, the software needs to only vary the time the signal is at 5 V with respect to the time the signal is at 0 V to achieve any desired voltage between 0 V and 5 V.

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