CMOS Asynchronous Communications Element# CP82C50A5 Programmable Communications Interface Technical Documentation
Manufacturer : INTERSIL
## 1. Application Scenarios
### Typical Use Cases
The CP82C50A5 serves as a programmable asynchronous communications interface, primarily functioning as a Universal Asynchronous Receiver/Transmitter (UART) in embedded systems. Key applications include:
- Serial Data Communication : Converts parallel data from microprocessors to serial data streams and vice versa
- Modem Control : Interfaces with modems through standard RS-232 signaling
- Industrial Control Systems : Facilitates communication between central processors and peripheral devices
- Data Logging Equipment : Manages serial data transmission to storage devices and displays
### Industry Applications
- Telecommunications : Used in modem interfaces, multiplexers, and communication controllers
- Industrial Automation : Implements serial communication in PLCs, SCADA systems, and process control equipment
- Medical Devices : Enables serial communication in patient monitoring equipment and diagnostic instruments
- Point-of-Sale Systems : Handles communication between terminals and peripheral devices like receipt printers
- Embedded Systems : Provides serial interface capabilities in microcontroller-based applications
### Practical Advantages and Limitations
Advantages:
- Programmable Features : Configurable baud rates (50-19.2K baud), character length, stop bits, and parity
- Hardware Compatibility : Direct interface with most 8-bit and 16-bit microprocessors
- Low Power Consumption : CMOS technology ensures efficient power usage
- Built-in Diagnostics : Local loopback capability for system testing
- Reliable Operation : Includes false start bit detection and break character generation
Limitations:
- Limited Baud Rates : Maximum 19.2K baud may be insufficient for high-speed applications
- Legacy Architecture : Lacks modern features like hardware flow control or FIFO buffers
- Component Count : Requires external crystal oscillator and supporting discrete components
- Obsolete Technology : Being superseded by more integrated solutions in modern designs
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Incorrect Clock Configuration
- Issue : Using inappropriate crystal frequencies or improper divider settings
- Solution : Calculate baud rate using formula: Baud Rate = Clock Frequency / (16 × Divisor)
- Implementation : Use 1.8432 MHz or 3.072 MHz crystals for standard baud rates
Pitfall 2: Signal Integrity Problems
- Issue : Noise and signal degradation in long-distance serial communication
- Solution : Implement proper line drivers (MAX232 for RS-232) and filtering capacitors
- Implementation : Place 0.1μF decoupling capacitors close to power pins
Pitfall 3: Interrupt Handling Issues
- Issue : Lost interrupts or incorrect priority handling
- Solution : Implement proper interrupt service routine with status register polling
- Implementation : Clear interrupt sources promptly and use edge-triggered interrupt inputs
### Compatibility Issues with Other Components
Microprocessor Interface:
- Direct Compatibility : 8085, Z80, 6800 series microprocessors
- Bus Timing : Requires address decoding logic and proper timing alignment
- Voltage Levels : 5V operation compatible with TTL and CMOS logic families
Peripheral Integration:
- Line Drivers : Compatible with RS-232 (MAX232), RS-422 (AM26LS31), and RS-485 drivers
- Modem Interfaces : Standard modem control signals (DTR, DSR, RTS, CTS)
- Clock Sources : Requires external crystal oscillator or clock generator
### PCB Layout Recommendations
Power Distribution:
- Use star-point grounding for analog and digital sections
- Implement 0.1μF ceramic capacitors at each power
