September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Mitsubishi MELPS740/WDC W65CO2S
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Although the Mitsubishi MELPS740, for which there are more than 600 parts, is a redesign of Western Design Center's (WDC) 6502, the two architectures have many similarities. The accumulator-based 740 and W65C02S have 71 instructions, an 8-bit accumulator, and two 8-bit index registers. The stack pointer is 8 bits wide; the program counter is 16 bits wide. The CPU is semipipelined: It fetches the next instruction while decoding and executing the current instruction. With a relatively fast memory interface, this feature lets code use part of internal RAM as a large register set to hold dynamic variables.

The 740 and W65C02S have a 64-kbyte unified address space, which divides into 256-byte pages for X and Y indexing. Page 0 is the first page in memory, and you can easily address it using special address modes and instructions. The chip has a fast, nonmultiplexed external bus—16 bits for addresses and 8 bits for data.

WDC's 16-bit extension of the W65C02S, the W65C816S, has a 6502-emulation mode that lets the W65C816S directly execute 6502 object code. The extended versions have a 16-bit accumulator, an index, and a stack-pointer register. The W65C816S also adds 78 operation codes, nine addressing modes, and a second 8-bit accumulator. Mitsubishi also extends the architecture to 16 bits with the 7700 series.

The W65C816S addresses as much as 16 Mbytes; the W65C02S has a 64-kbyte limit. The 16-bit CPU generates a 24-bit address by concatenating the 16-bit program or calculated address with an 8-bit bank register. (The W65C02S reserves separate bank registers for program and data.)

Power management: The devices have stop and wait low-power modes. Most of the M38XXX products support key-on- wake-up (K-O-W), a method of recovering from a low-power-consumption or sleep mode. When the system is idle, K-O-W can place it in sleep mode. During the sleep mode, the internal clock stops and thereby reduces power consumption while retaining its memory and status. When the system uses K-O-W, any key a user presses calls an interrupt that restarts the clock, waking the system back to its normal mode, which is transparent to the user. WDC's W65C134S and W65C265S microcontrollers have power-management features, which built-in monitor ROMs control.

Special instructions: The W65C02S and 740 support bit-manipulation instructions that include set, clear, test, complement, and branch if bit is 0 or 1. Math functions include add, subtract, increment, decrement, and decimal adjust. STP stops the clock; Wait waits for an interrupt. The 816S performs block moves.

Special on-chip peripherals: The M376XX devices support an internal charge pump that allows the µC to perform voltage conversions. You can interface these µCs to external devices with different voltage requirements without extra hardware. The M37630 contains a module to support the Basic-CAN version 2.0B protocol. The M37640 supports a 12-Mbps Universal Serial Bus (USB) hub or a single application. This device has the D+ and D- reference voltage for direct USB communications to the host or another hub. The M37690M8 supports General Magic's (www.generalmagic.com) proprietary serial-bus format, Magicbus.

Development tools: Mitsubishi's PC4701 emulator provides real-time debugging for the 740-series products. The emulator operates with PC-compatible software to control target-system debugging. The software provides a multiwindow development environment. IAR Systems (www.iar.com), 2500AD (www.2500ad.com), and ByteCraft (www.bytecraft.com) offer C compilers.

WDC provides a software-development system (SDS). The W65C02S core in the W65C134S microcontroller and the W65C816S core in the W65C265S microcontroller have embedded monitors that aid in debugging with the SDS. Also, the monitor ROMs have libraries for onboard I/O, timers, UART, and power management. Avocet (www.avocetsystems.com) and Universal Cross Assembler (http://ourworld.compuserve.com/homepages/UCA/) provide compilers for WDC. Other third-party vendors supply hardware-development tools. (Visit www.wdesignc.com/develop.html.)

Second sources: There are no second sources for the Mitsubishi series. Sanyo (www.sanyo.com) is a second source for the WDC products.

For details on devices in these families,
search EDN's Microprocessor Database:

Mitsubishi MELPS740	WDC WDC65C02

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