September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

NEC K Series
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The NEC K Series comprises the K0, K0S, and K4 families, all of which derive from a common architecture. NEC's K0 family, with more than 200 versions, represents the backbone of the K series. The K4 family provides a 16-bit upgrade path and a superset of the K0 instruction set, and the K0S has a subset of the K0 instruction set and only one register bank. K0S devices feature smaller ROM, RAM, and package combinations and no multiply/divide.

The K0 family has a 16-bit program counter and stack pointer and an external addressing range as large as 60 kbytes. K0 devices have four sets of working register banks to support context switching. Each register bank contains eight 8-bit registers, which you can pair to function as four 16-bit registers. The register banks are in on-chip RAM along with directly addressable RAM. The CPU symbolically addresses the registers as the current register bank or as memory.

The K4 has eight register banks and four additional working registers, which you can combine with the 8-bit extension registers to access a 24-bit address space. Each register bank contains 16 8-bit registers, which you can pair to function as 16-bit registers. NEC packs as much as 256 kbytes of ROM and as much as 13 kbytes of RAM into its K4 devices. The K4's interrupt structure adds a macro-service function and hardware support for context switching. For context switching with the K4 family, you can specify a register bank to dedicate to a specific interrupt. The macro service allows a DMA type of operation to service peripherals, such as the serial port or real-time output port. The K0's interrupt structure supports prioritized vectored interrupts and software context switching. You accomplish the context switch with a register-bank-select instruction after branching to the interrupt-service routine.

You can access on-chip, memory-mapped peripherals by main-memory addressing or by special-function-register addressing. The K Series devices have two RAM areas. A high-speed RAM area of up to 1 kbyte includes 32 8-bit registers and general-purpose RAM. Devices with larger ROM sizes have an additional internal-expansion-RAM area of up to 1 kbyte. In addition to data storage, you can use the internal expansion RAM to hold executable instruction code.

K4 µCs contain a 3-byte instruction-prefetch queue. The bus-control unit can fetch an instruction byte from memory during cycles in which the execution unit is not using the memory bus.

Power management: Halt mode discontinues CPU operation while all peripherals continue to operate. In stop mode, only the subsystem clock (if used) and interrupts operate. The K4 has an idle mode in which the oscillation circuitry continues to operate but the entire system stops. All K Series devices have a programmable clock divider to conserve power during less demanding operations. You can also run the K Series devices on a 32-kHz subsystem clock, which allows the microcontroller to stop the main clock and continue to execute code.

Special instructions: Bit-manipulation instructions are bit set, clear, complement, test, and various logic operations. Math instructions include add, subtract, multiply, divide, and decimal adjust. K0 CPUs handle 16-bit operations by pairing adjacent registers in banks. Their 16-bit arithmetic operations include add and subtract word and increment and decrement word. K0 and K4 Series µCs can perform an 8X8-bit multiply and a 16X8-bit divide. Hardware implements a 64-byte call address table that adds a level of indirection to branches and subroutine calls. This option is useful when making frequent calls to specific subroutines because the call instruction (CALLT) is a 1-byte instruction versus a standard 3-byte call to a direct address.

Development tools: K Series development tools include Windows-interface-controlled emulators. The interface incorporates a project manager to allow a user to write, execute, debug, and trace code; examine registers and memory; and perform other tasks. The user can handle all development functions from within the project manager. Additional elements of the development environment include, low-cost evaluation boards and one-time-programmable and flash-based devices. NEC also offers software system simulators for code development. This simulator contains a window interface to enable input from components such as switches and potentiometers, along with output from components such as LCDs, LEDs, and motors. You may also create your own components. Additionally, the simulator supports application operations with C++ or Visual Basic modules and with debugging capability.

Second sources: There are no second sources for the K Series.

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