Technical Summary: HC705DX Microcontroller Family

Overview

The HC705DX is a family of 8-bit microcontrollers from Motorola (now NXP) featuring the M68HC05 CPU core. These devices are designed for embedded control applications requiring low power consumption, flexible I/O capabilities, and robust peripheral integration. The family includes several variants (MC68HC05D24, MC68HC05D32, and MC68HC705D32) with varying memory sizes and feature sets.

Key aspects of the HC705DX architecture include:

• 8-bit M68HC05 CPU core with enhanced instruction set
• On-chip memory (ROM/OTP/EPROM variants available)
• Multiple operating modes for power management
• Comprehensive peripheral set including timers, serial interfaces, and PWM
• Industrial temperature range support

Features

Core Features

• 8-bit M68HC05 CPU core
• Up to 2MHz operating frequency
• 16-bit stack pointer
• 63 basic instructions
• 11 addressing modes

Memory Features

• Up to 32KB program memory (variant dependent)
• 256B to 1KB RAM (variant dependent)
• Memory-mapped I/O registers
• Security features to protect program memory

Peripheral Features

• Multiple parallel I/O ports (up to 40 I/O lines)
• 16-bit programmable timer with input capture/output compare
• Serial Communications Interface (SCI)
• 8-bit Pulse Width Modulation (PWM) unit
• On-chip oscillator with crystal driver

Power Management

• WAIT and STOP low-power modes
• Clock prescaler for power optimization
• Full static operation for low-frequency applications

Applications

The HC705DX family is suitable for a wide range of embedded control applications including:

• Industrial control systems
• Automotive electronics
• Consumer appliances
• Security systems
• Medical devices
• HVAC controls
• Power management systems

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage: -0.3V to +7.0V
• Input Voltage: -0.3V to VDD+0.3V
• Operating Temperature Range: -40°C to +85°C
• Storage Temperature Range: -55°C to +150°C

Recommended Operating Conditions

• Supply Voltage: 3.0V to 5.5V
• Operating Frequency: DC to 2.1MHz
• Input High Voltage: 0.7VDD to VDD
• Input Low Voltage: VSS to 0.3VDD

Power Consumption

• Active Mode (2.1MHz): 5mA typical
• WAIT Mode: 1.5mA typical
• STOP Mode: 10μA typical

Timing Characteristics

• Instruction Cycle Time: 2μs at 2.1MHz
• Reset Pulse Width: 1.5μs minimum
• Timer Resolution: 500ns at 2.1MHz

Package Information

Available Packages

• 40-pin Plastic Dual In-line Package (PDIP)
• 44-pin Plastic Leaded Chip Carrier (PLCC)
• 48-pin Quad Flat Package (QFP)

Pin Descriptions

The HC705DX features multiple functional pin groups:

Power Pins

• VDD: Main power supply (3.0-5.5V)
• VSS: Ground reference

Clock Pins

• OSC1: Crystal oscillator input
• OSC2: Crystal oscillator output

Control Pins

• RESET: Active-low reset input
• IRQ: Maskable interrupt input

I/O Ports

• Port A: 8-bit general purpose I/O
• Port B: 8-bit general purpose I/O
• Port C: 8-bit general purpose I/O (alternate functions)
• Port D: 6-bit general purpose I/O

Ordering Information

The HC705DX family is available in multiple variants with different memory configurations:

Development Support

Motorola/NXP provides comprehensive development support for the HC705DX family:

• Evaluation boards and development kits
• In-circuit emulators
• C compilers and assemblers
• Debugging tools
• Application notes and reference designs

Conclusion

The HC705DX microcontroller family offers a cost-effective solution for embedded control applications requiring an 8-bit architecture with robust peripheral integration. With multiple memory options, package variants, and low-power operating modes, these devices provide design flexibility for a wide range of applications. The mature HC05 architecture ensures reliable operation and extensive development support.