September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Motorola 68HC11
	View block diagram

The 68HC11 has two 8-bit accumulators, an 8-bit condition-code register, two 16-bit index registers, a 16-bit stack pointer, and a 16-bit program counter. The CPU can address the two accumulators as a 16-bit accumulator. In addition to executing all instructions in the M6800 and M6801, the 68HC11 includes 91 new options in its instruction set.

The 68HC11 restricts addressing to a 64-kbyte unified address space. Some versions have a memory-extension unit that expands addressing to 1 Mbyte using bank-switched paging. Two memory windows in the 64-kbyte address space map into a 1-Mbyte space. The CPU can directly access memory-mapped I/O (on-chip peripherals).

The 68HC11s run in single-chip mode using only on-chip memory resources or in expanded mode. Expanded mode replaces some I/O ports with an address/data bus to access external memory. Both multiplexed and nonmultiplexed external-bus versions are available. Some versions have programmable chip selects.

Power management: Wait mode discontinues CPU processing but leaves the clock, timer, serial-peripheral-interface, and serial-communications-interface systems enabled. Stop mode stops the clock and all internal processing. Both modes maintain RAM and enable interrupt to wake the CPU. You can program and selectively turn off most peripherals.

Special instructions: The 68HC11's bit-manipulation instructions are bit set, clear, test, and jump if bit is set or clear. Math functions include add, subtract, increment, decrement, divide, and multiply. Instructions also swap accumulators, exchange an accumulator and an index register, transfer stack pointer+1 to an index register, and set the stack pointer from an index register. A wait-for-interrupt instruction increments the program counter, puts all registers on the stack, halts, and waits for an interrupt.

Development tools: Many tools, including assemblers, compilers, and debuggers from third-party vendors, support the HC11 family. Nine vendors offer RTOSs for the HC11, 23 offer emulators, six offer evaluation boards, and 15 supply programmers.

Second sources: Toshiba acts as a second source for some A and E series devices.

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