Freescale 68HC11

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The 68HC11 (6811 or HC11 for short) is a microcontroller (µC) family originally from Motorola, now produced by Freescale Semiconductor, descended from the Motorola 6800 microprocessor. The 68HC11 devices are more powerful and more expensive than the 68HC05 microcontrollers, and are used in barcode readers, hotel card key writers, and various other embedded systems.

The MC68HC11A8 is available in a 48-pin dual in-line package (DIP), as well as the 52-pin plastic leaded chip carrier (PLCC) as shown above.

Internally, the HC11 instruction set is upward compatible with the 6800, with the addition of a Y index register. (Instructions using the Y register have opcodes prefixed with the byte 0x18). It has two eight-bit accumulators, A and B, two sixteen-bit index registers, X and Y, a condition code register, a 16-bit stack pointer, and a program counter. In addition, some instructions treat the A and B registers as a combined 16-bit D register.

Different versions of the HC11 have different numbers of external ports, labeled alphabetically. The most common version has five ports, A, B, C, D, and E, but some have as few as 3 ports (version D3). Each port is eight-bits wide except for D, which is six bits (in some variations of the chip, D also has eight bits). It can be operated with an internal program and RAM (1 to 768 bytes) or an external memory of up to 64 kilobytes. With external memory, B and C are used as address and data bus. In this mode, port C is multiplexed to carry both the lower byte of the address and data.

A MC68HC24 port replacement unit is available for the HC11. When placed on the external address bus, it replicates the original functions of B and C. Port A has input capture, output compare, pulse accumulator, and other timer functions; port D has serial I/O, and port E has an analog to digital converter (ADC).

The popular Handy Board robotics controller is based on the 68HC11.