September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Mitsubishi MELPS7700
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Mitsubishi's MELPS7700 µC family has more than 100 products, which cover commercial and industrial applications. With 109 instructions, the MELPS7700 architecture builds on the basic MELPS740 instruction set and architecture. The accumulator-based CPU has two 16-bit accumulators, two 16-bit index registers, and a 16-bit program counter and stack pointer. Two bus rails feed directly into the ALU. The accumulators, index registers, program counter, stack pointer, program- and data-bank registers, and a 24-bit address incrementer lie between the bus rails. Almost all operations pass through the accumulator. The main registers can function as 8- or 16-bit registers.

The semipipelined 7700's CPU fetches the next instruction while executing the current one. A 3-byte prefetch queue holds the next instruction. More than 90% of the instructions execute in less than 1 µsec at 25 MHz. The 16-Mbyte address space divides into 256 64-kbyte banks. The high-order bits of a 24-bit address reference the bank; an 8-bit program- or data-bank register supplies this field. Bank 0 holds the special-function registers, internal RAM, and internal ROM. In single-chip mode, executing from on-chip ROM and RAM, the CPU has only one 64-kbyte bank. For debugging, the chip can run in µP mode, in which it executes from off-chip program memory.

The 7700 has a 256-byte "direct page" for time-critical routines. This page can lie in the first 64-kbyte memory bank or between the first and second banks. The 16-bit direct-page register points to the base (lower) address of the direct page. Accessing the direct page using the direct-page register is faster and takes only 2 bytes.

The external-memory bus can be multiplexed or demultiplexed. For a 16-bit address, the bus is nonmultiplexed; it uses 16-bit addresses and 8-bit data. The CPU can access 16-bit data from odd or even bytes, but performance degrades when using an odd byte.

Power management: During wait, oscillation continues, and the integrated peripherals are active. In stop, oscillation stops, and most peripherals are disabled.

Special instructions: The 7700's bit-manipulation instructions include bit set, clear, and test for certain flag bits. Math instructions include unsigned multiply and divide, add, subtract, and decimal adjust. The M377XX performs register A and B exchange and a forced execution breakpoint.

Special on-chip peripherals: The M37750F6BFP contains 48 kbytes of 12V flash memory. Some devices, such as the M3807X and M3820X, include real-time ports that you can use to send data out to external devices for a specific number of clock cycles, thus creating precise control for applications such as printer-head control and paper positioning in a laser printer.

The M3807X group of devices contains PWMs that you can use to control stepper motors of two, three, or four phases. These PWMs use a single multiplexed output line to control the other coils within the motor. The PWMs' outputs depend on the values of dedicated registers that determine the high and low periods. Most of the MELPS7700 devices support a main clock and a 32-kHz subclock. The main clock allows the device to operate at full speed when it needs to perform calculations or port operations.

Development tools: Third-party development tools for the MELPS7700 include the Ashling (www.ashling.com) Ultra-7700 µP-development system, which comprises an in-circuit emulator and the PathFinder-7700 for Windows source-level debugger. Hewlett-Packard (www.hp.com) provides the 64147A emulator for real-time measurements. IAR's (www.iar.com) C compiler supports both of these emulators. Additional development tools include the Lauterbach (www.lauterbach.com) Trace 32 and Accelerated Technology's (www.atinucleus.com) Nucleus RTOS. ByteBos (www.bytebos.com) offers a multitasking RTOS for Mitsubishi's M377XX µCs. Orion Instruments (www.yokogawa.com) offers the ADViCE emulation systems hosted by Microview G, a graphical high-level debugger and in-circuit-emulator interface.

Second sources: There are no second sources for the 7700.

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