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PIC12CE673 数据表(PDF) 7 Page - Microchip Technology |
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PIC12CE673 数据表(HTML) 7 Page - Microchip Technology |
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7 / 116 page ![]() © 1998 Microchip Technology Inc. Preliminary DS40181B-page 7 PIC12CE67X 3.0 ARCHITECTURAL OVERVIEW The high performance of the PIC12CE67X family can be attributed to a number of architectural features com- monly found in RISC microprocessors. To begin with, the PIC12CE67X uses a Harvard architecture, in which program and data are accessed from separate memo- ries using separate buses. This improves bandwidth over traditional von Neumann architecture in which pro- gram and data are fetched from the same memory using the same bus. Separating program and data buses also allow instructions to be sized differently than the 8-bit wide data word. Instruction opcodes are 14- bits wide making it possible to have all single word instructions. A 14-bit wide program memory access bus fetches a 14-bit instruction in a single cycle. A two- stage pipeline overlaps fetch and execution of instruc- tions (Example 3-1). Consequently, all instructions (35) execute in a single cycle (400 ns @ 10 MHz) except for program branches. The table below lists program memory (EPROM), data memory (RAM), and non-volatile memory (EEPROM) for each PIC12CE67X device. Device Program Memory RAM Data Memory EEPROM Data Memory PIC12CE673 1K x 14 128 x 8 16x8 PIC12CE674 2K x 14 128 x 8 16x8 The PIC12CE67X can directly or indirectly address its register files or data memory. All special function regis- ters, including the program counter, are mapped in the data memory. The PIC12CE67X has an orthogonal (symmetrical) instruction set that makes it possible to carry out any operation on any register using any addressing mode. This symmetrical nature and lack of ‘special optimal situations’ make programming with the PIC12CE67X simple yet efficient. In addition, the learn- ing curve is reduced significantly. PIC12CE67X devices contain an 8-bit ALU and work- ing register. The ALU is a general purpose arithmetic unit. It performs arithmetic and Boolean functions between the data in the working register and any regis- ter file. The ALU is 8-bits wide and capable of addition, sub- traction, shift and logical operations. Unless otherwise mentioned, arithmetic operations are two's comple- ment in nature. In two-operand instructions, typically one operand is the working register (W register). The other operand is a file register or an immediate con- stant. In single operand instructions, the operand is either the W register or a file register. The W register is an 8-bit working register used for ALU operations. It is not an addressable register. Depending on the instruction executed, the ALU may affect the values of the Carry (C), Digit Carry (DC), and Zero (Z) bits in the STATUS register. The C and DC bits operate as a borrow bit and a digit borrow out bit, respectively, in subtraction. See the SUBLW and SUBWF instructions for examples. |
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