Motorola 68HC11
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MC68HC11_microcontroller.jpg
The Motorola 68HC11 (6811 or HC11 for short) is a microcontroller (µC) family from Motorola, descended from the Motorola 6800 microprocessor, and a subfamily of the 68h family. 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.
Internally, the HC11 instruction set is upward compatible with the 6800, with the addition of a Y index register. (Instructions using the Y register are prefixed with byte such as 0x18). It has two eight-bit accumulators, A and B, two sixteen-bit index registers, X and Y, a processor flag 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.
The HC11 has five external ports, A, B, C, D, and E. 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).
- This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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