September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Motorola 68HC05
	View block diagram

More than 180 versions of the 68HC05 are available. The accumulator-based low-end 68HC05 µC has few registers and a stripped-down 6800 instruction set with 64 instructions. The instruction set features 10 uncomplicated addressing modes, including 8- and 16-bit indexing from the 16-bit program counter. The 68HC05 architecture can directly access a maximum of 64 kbytes; you can use paging to access additional memory. In addition to the accumulator, the CPU's core has an index register, a 5-bit stack pointer, and a 5-bit condition-code register.

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

Special instructions: The 68HC05's bit-manipulation instructions are set, clear, test, jump on bit set, or jump on bit clear. The CPU can test and branch on an interrupt bit, but branches are 5127 bytes relative to the program counter. Math functions include add, subtract, increment, decrement, and multiply.

Special on-chip peripherals: The 68HC05's timer/ counter is built around a 16-bit free-running counter, which is coupled with a 16-bit capture register and a 16-bit compare register. The capture register captures timer values on some line events; the timer/counter continually compares the compare register with the running timer. When the registers match, an output compare flag is set, and an output pin is driven to a programmed value. The 68HC705V8 and 68HC05V7 contain a voltage regulator that provides 5V directly from a 12V battery. The 68HC705JB2 and 68HC908KW12 include Universal Serial Bus support with a 3.3V bandgap reference that helps reduce costs by eliminating an external voltage regulator. The 68HC08AZ family includes Motorola's scalable controller-area network (MSCAN), which supports 2.0A and 2.0B specs with a prioritization scheme that allows determination of maximum wait time for each CAN message.

Development tools: Many third-party development tools are available for the 68HC05. These tools include compilers, source-level debuggers, a PC-based software simulator, production programmers, evaluation systems, and in-circuit emulators. Visit the Motorola Web site at http://sps.motorola.com/csic for a listing of available products.

Second sources: Harris Semiconductor supports some versions.

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