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 barcode readers, hotel card key writers, amateur robotics, 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 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.
The standard bootloader for the HC11 family is called BUFFALO, "Bit User Fast Friendly Aid to Logical Operation" (a BUFFALO prompt seen on the serial port at bootup is a sign that a board's flash memory has been erased). Not all HC11 models come with the BUFFALO bootloader. The 68HC11A0 and A1 do not but the A8 does.
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 Freescale 68HC12 is an enhanced 16-bit version of the 68HC11.
The Freescale 68HC16 microcontroller is intended as a 16-bit mostly software compatible upgrade of the 68HC11.
The Handy Board robotics controller by Fred Martin is based on the 68HC11.
Full article ▸