RabbitCore RCM2300 User's Manual

> ## Appendix D. Sample Circuits

> This appendix details several basic sample circuits that can be used with the RCM2300.

> - RS-232/RS-485 Serial Communication
> - Keypad and LCD Connections
> - External Memory
> - D/A Converter

> ### D.1 RS-232/RS-485 Serial Communication

> Figure D-1. Sample RS-232 and RS-485 Circuits

> Sample Program: PUTS.C in SAMPLES/RCM2300.

> ### D.2 Keypad and LCD Connections

> Figure D-2. Sample Keypad Connections

> Sample Program: KEYLCD.C in SAMPLES/RCM2300.

> Figure D-3. Sample LCD Connections

> Sample Program: KEYLCD.C in SAMPLES/RCM2300. (When Parallel Port A is not being used for quick communication, its resting, quiescent value is used to set the LCD contrast level.)

> ### D.3 External Memory

> The sample circuit can be used to access 16 bytes on an external 64K memory device. Larger SRAMs can be written to using this scheme by using other available Rabbit 2000 ports (parallel ports A to E) as address lines.

> Figure D-4. Sample External Memory Connections

> Sample Program: EXTSRAM.C in SAMPLES/RCM2300.

> ### D.4 D/A Converter

> The output will initially be 0 V to -10.05 V after the first inverting op-amp, and 0 V to +10.05 V after the second inverting op-amp. All lows produce 0 V out, FF produces 10 V out. The output can be scaled by changing the feedback resistors on the op-amps. For example, changing 5.11 kW to 2.5 kW will produce an output from 0 V to -5 V. Op-amps with a very low input offset voltage are recommended.

> Figure D-5. Sample D/A Converter Connections

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