Appendix D. Sample Circuits

Appendix D provides these sample circuits that incorporate the RCM2000.

· RS-232/RS-485 Serial Communication

· Keypad and LCD Connections

· LCD Connections

· External Memory

· Simple 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/SERIAL.

D.2 Keypad and LCD Connections

Figure D-2. Sample Keypad Connections

Sample Program: KEYLCD.C in SAMPLES/COREMODULE.

Figure D-3. Sample LCD Connections

Sample Program: KEYLCD.C in SAMPLES/COREMODULE.

D.3 LCD Connections

Figure D-4. Sample LCD Connections

Sample Program: LCD_DEMO.C in SAMPLES/COREMODULE.

The shaded part of the circuit in Figure D-4 can be used to drive a second LCD, but additional software not included in LCD_DEMO.C will have to be written.

D.4 External Memory

The sample circuit can be used with an external 64 Kbit 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-5. Sample External Memory Connections

Sample Program: EXTSRAM.C in SAMPLES/COREMODULE.

D.5 Simple 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 (first stage) and 0 V to 5 V (second stage). Op-amps with a very low input offset voltage are recommended.

Figure D-6. Sample D/A Converter Connections

A sample program is not available at this time.