September 24, 1998

EDN's 25th Annual Microprocessor/Microcontroller Directory

Philips 80C51XA
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The 16-bit architecture of Philips' 80C51XA is compatible with and shares the programmer's model of the 8051. Operation centers on a 21-word register file. You access these registers, which can perform all ALU functions, as words, bytes, or individual bits. Some instructions, such as 32-bit shifts, multiplies, and divides, allow addressing pairs of word registers as double words. The XA architecture supports as many as 32 maskable interrupts and has exception-handling circuitry for fault-tolerant systems. The architecture also supports multitasked applications and handles as many as 255 independent tasks.

The XA-S3's 24-bit program counter provides addressing for as much as 16 Mbytes of linear code space; other XA derivatives address only as much as 1 Mbyte. The prefetch queue holds the next instruction to be executed, improving the instruction-execution performance. The XA's memory structure is the same as that of the 80C51. It has separate data-memory and special-function-register (SFR) spaces. The XA divides its 16-Mbyte data-memory space into 256 64-kbyte segments. The SFRs have the same role in the XA as in the 80C51: controlling and monitoring the on-chip peripheral functions. The XA's stack resides in the data-memory space and can be as large as 64 kbytes. The stack can reside in the on- or off-chip memory space or both on and off chip.

The external-memory interface supports the 24-bit memory address, and you can configure it for 8- or 16-bit accesses. At power-on or dynamically under software control, you can configure the data-bus width for 8- and 16-bit accesses. Programmable wait states help you control external-memory accesses, and a wait pin allows easy interfacing to external memory and other devices.

Power management: A software-controlled idle mode shuts down processor functions but leaves most of the on-chip peripherals and external interrupts functioning; power-down mode shuts down everything, including the on-chip oscillator.

Special instructions: The XA supports all of the 80C51 instructions and a variety of new instructions to benefit C programming. The XA performs extensive bit manipulation with instructions such as jump on bit set or clear, set, clear, move, AND, and OR. Math instructions include add, subtract, 16X16-bit multiplication, signed and unsigned 32X16-bit divide, and 32-bit shifts. The XA also has instructions to normalize and sign-extend operands for floating-point support, move data blocks, jump double indirect, breakpoint and trap, and reset.

Special on-chip peripherals: The XA-S3 derivatives have an eight-channel, 10-bit A/D converter with automatic channel-scan and repeat functions. They also contain a five-channel, 16-bit programmable counter array.

Development tools: Third-party development tools from many vendors support the XA. These tools include assemblers, simulators, C compilers, RTOSs, in-circuit emulators, EPROM programmers, development boards, and adapter sockets. Philips' $499 EB-XA emulator serially links to a PC and can emulate in ROMless or ROM mode. The emulator uses a Philips bond-out chip that emulates the µC and reveals the internal resources to the user. The EB-XA supports debugging and breakpoints and allows real-time execution of XA code.

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

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