NXP Semiconductors MC68HC705C8ACFB

Overview

MC68HC705C8ACFB from Freescale Semiconductor is an 8-bit OTP microcontroller with 8 KB on-chip EPROM/OTPROM, 192 bytes RAM, and integrated peripherals including SCI, SPI, and a 16-bit capture/compare timer. It operates at up to 4 MHz (5 V) or 2 MHz (3.3 V), supports multiple low-power modes (Stop, Wait, Data-Retention), and targets embedded control in industrial sensors and legacy automotive subsystems.

For engineers reviewing the MC68HC705C8ACFB datasheet, MC68HC705C8ACFB pinout, MC68HC705C8ACFB application, or MC68HC705C8ACFB equivalent, key selection criteria include OTP memory retention, 40-pin PDIP package compatibility, COP watchdog configurability, and dual-voltage (5 V / 3.3 V) operation support for legacy system upgrades.

Technical Context

The MC68HC705C8ACFB implements the M68HC05 CPU core with 8-bit ALU, 16-bit program counter, and condition code register. Its memory architecture includes 8 KB of one-time-programmable EPROM, 192 bytes of static RAM, and dedicated bootloader ROM for in-system programming via SCI.

Peripheral integration includes full-duplex Serial Communications Interface (SCI) with programmable baud rate, master/slave Serial Peripheral Interface (SPI), and a 16-bit timer supporting input capture (edge-triggered event timing) and output compare (PWM generation). Reset sources include power-on reset, external RESET pin, and both programmable and non-programmable COP watchdog timers.

Key Specifications

Pinout & Package

The MC68HC705C8ACFB is packaged in a 40-pin Plastic Dual In-Line Package (PDIP), Case #824E per Motorola mechanical spec. Pin assignments follow standard HC05 layout with VDD/VSS power pins, OSC1/OSC2 for crystal/resonator clock source, RESET, IRQ, TCAP, TCMP, and four 8-bit parallel I/O ports (PA–PD).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microcontroller applications.

Compared with MC68HC705P6ACFB, the MC68HC705C8ACFB provides double the program memory and adds SPI for peripheral expansion; versus MC68HC705B16CFB, it trades memory capacity and advanced timer modes for lower cost and 40-pin PDIP compatibility in space-constrained legacy PCBs.

Availability

MC68HC705C8ACFB is available at Aetrix Electronics and suitable for industrial sensor nodes, legacy automotive subsystems, appliance motor controllers, and point-of-sale peripheral interfaces requiring stable component supply across extended production lifecycles.

Supply support for MC68HC705C8ACFB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Freescale Semiconductor (now part of NXP Semiconductors) was a leading designer of embedded processors and analog/mixed-signal ICs, known for the 68HCxx family of microcontrollers targeting cost-sensitive industrial and automotive applications.

The MC68HC705C8ACFB belongs to the M68HC05 microcontroller product line, designed specifically for low-cost, low-power embedded control where OTP firmware security and minimal external components were critical design requirements.

FAQ

What is the maximum operating frequency of the MC68HC705C8ACFB?

The MC68HC705C8ACFB operates at up to 4 MHz when powered at 5.0 V, and up to 2 MHz at 3.3 V. These frequencies are specified in Section 13.7 and 13.8 of the Rev. 3 datasheet and define the upper limit for instruction execution and peripheral timing. Exceeding these values risks setup/hold violations in internal logic and may cause undefined behavior. The MC68HC705C8ACFB does not support dynamic frequency scaling - clock speed is fixed by the external crystal or resonator selected.

Does the MC68HC705C8ACFB support in-circuit programming after soldering?

Yes, the MC68HC705C8ACFB supports in-system programming (ISP) via its Serial Communications Interface (SCI) using the on-chip bootloader ROM. Programming requires applying VPP (12.5 V) to Pin 1 (VPP) during entry into programming mode, then sending Intel Hex records through SCI. This capability is documented in Section 9.3 and Appendix A of the Rev. 3 datasheet and enables firmware updates without removing the MC68HC705C8ACFB from the target board.

What are the key differences between the MC68HC705C8ACFB and MC68HC705B16CFB?

The MC68HC705C8ACFB has 8 KB of OTPROM and uses a 40-pin PDIP package, while the MC68HC705B16CFB offers 16 KB OTPROM and is housed in a 44-pin PLCC. The B16 variant adds modulo counting to its timer and supports higher-speed operation. Both share the same M68HC05 core and peripheral set (SCI, SPI, COP), but the MC68HC705C8ACFB is optimized for cost and footprint in less demanding applications where 8 KB firmware suffices.

Can the MC68HC705C8ACFB operate from a 3.3 V supply without level shifters?

Yes, the MC68HC705C8ACFB is fully specified for 3.3 V ±10% operation per Section 13.8 of the Rev. 3 datasheet. All I/O pins are 3.3 V tolerant, and internal logic levels scale accordingly. No level shifters are required when interfacing with other 3.3 V peripherals. However, the VPP programming voltage remains 12.5 V regardless of VDD - external circuitry must still generate this voltage during programming sequences.

How does the COP watchdog function differ between programmable and non-programmable modes on the MC68HC705C8ACFB?

The MC68HC705C8ACFB implements two COP watchdog configurations: programmable (user-selectable timeout via COPRST register) and non-programmable (~16 ms fixed timeout). In programmable mode, the COP reset interval is set by writing to COPRST; in non-programmable mode, the COP resets the MCU if not cleared within ~16 ms, independent of software configuration. Both modes are enabled via Option Register bits and coexist - the MC68HC705C8ACFB resets if either watchdog expires unacknowledged.