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