The Design Of An 8-bit MCU

Nowadays, an 8-bit MCU with RISC core is widely applied in industrial control field. To satisfy various actual requirements, MCU has great development towards low power consumption, high speed and low cost.In this paper, an 8-bit MCU with a RISC instruction sets is presented, which consists of a micro-controller and peripherals. The micro-controller supports the logic function of 59 instructions, and peripherals are composed of two timers and the interrupt ruling system of five interrupt sources. For the design of micro-controller, in accordance with the design idea of CISC, we proposed to achieve part of double-cycle RISC instruction in the instruction set. The design is subdivided into two pipeline stages with Fetch and Execute.In the Execute stage, decoding instruction, reading source operands, ALU computation and writing results to the memory are accomplished by the micro-controller. Moreover, the ALU design learns the experience of the SN74181 technology, which accelerates the speed and reduces the circuit area. Therefore, the unique design thoughts about PC and PFLAG,which run as read-write and participate in the operation of each instruction, are proposed.The MCU verification platform of the system is also built in this paper. Firstly, all cases of each instruction are detailedly analyzed and the result in each case is verified. Then, to detect the possible conflicts by assembly instructions operation, six verification programs with C are provided. Coverage of each program reaches above 85%. Besides, according to the feature of operation code and the size of addressing space, the random verification platform is constructed. Thus, three groups of random data are given with the coverage of each group reaching above 90%. The accuracy of the random verification depends on the compared results of MODELSIM platform and hardware emulation platform. Furthermore,to verify that the design could be synthesized and satisfy the timing constraints, some verification of the MCU is carried out on FPGA, the model of which is SPARTAN-3E,with frequency 50 MHZ. Hence, a reliable MCU is obtained after a great deal of verification.