Motorola 68HC11

Motorola 68HC11 registers

15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 (bit position) Main registers A B D register pair Index registers IX X index register IY Y index register SP Stack Pointer Program counter PC Program Counter Status register   1 1 H I N Z V C Flags

The 68HC11 (6811 or HC11 for short) is an 8-bit microcontroller (µC) family introduced by Motorola in 1985. Now produced by Freescale Semiconductor, it descended from the Motorola 6800 microprocessor. It is a CISC microcontroller. The 68HC11 devices are more powerful and more expensive than the 68HC08 microcontrollers, and are used in automotive applications, barcode readers, hotel card key writers, amateur robotics, and various other embedded systems. The MC68HC11A8 was the first MCU to include CMOS EEPROM.

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, there is an 8 x 8-bit multiply (A x B), with full 16-bit result, and Fractional/Integer 16-bit by 16-bit Divide instructions. A range of 16-bit instructions treat the A and B registers as a combined 16-bit D register for comparison (X and Y registers may also be compared to 16-bit memory operands), addition, subtraction and shift operations, or can add the B accumulator to the X or Y index registers. Bit test operations have also been added, performing a logical AND function between operands, setting the correct conditions codes, but not modifying the operands.

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