For a detailed description of the display unit see

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Unformatted text preview: a detailed description of the display unit see Appendix F. 59 Figure 5.2: Block Diagram of Proc Module. 60 5-4. Processor Internal Components 5.4-1. EXTERNAL CONTROL SIGNALS As illustrated in Figure 5.2, the following control signals are provided externally to the processor core for its control and operational functionality. Resetp is an active hi input, when active; the processor is resetted and various variables are initialized to their starting default values. Similarly Holdp is an active low input, when active; only one instruction from memory is allowed to be executed. The Clockp is an externally generated clock signal that is crucial for the operation of all processor components. This signal oscillates at a frequency of 50 or 100 MHZ. All operations occur on the rising edge of the clock signal. 5.4-2. CONTROL UNIT The Control Unit is the brain of the RISC processor. It consists of numerous outputs and inputs to control the internal functions of the processor as illustrated in Figure 5.2. This unit has two main inputs; Count is the 4-Bit signal generated by the machine cycle counter and pcoutput is the 16-Bit instruction fetched from RAM. First different parts of the 16-bits instruction are decoded. After decoding, the Control Unit performs the required operation according to the decoded operand I. The Control Unit has two main outputs; Done is a 1-Bit active high signal, which shows the completion of an operation and EXE is a 8-Bit signal, which drives the value of data to be displayed on the external Seven Segment Display. The Clockp is generated external from the FPGA and driven through an I/O into the top module Proc. The Proc module includes the Control Unit code and instantiate all others sub modules named as pcounter, upcount, Ram, alu, Display, dll, regn and dec2to4. The Spartan-II family FPGA provides four dedicated DLLs for advanced clock domain control, zero propagation delay and low clock skew between output clocks signals distributed throughout the device. Therefore,...
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