opcodesubb.java

這是一個8051的模擬器 以java寫成

/**
 * Projet de langage JAVA IFITEP 3 2005 - Simulateur 8051 
 * <p> 
 * D閒inition de l'instruction SUBB.
 * Cf.:
 *  - documentation technique 8051
 *  - Ouvrage "Microcontroleur 8051 et 8052", edition Dunod
 *  
 * @author Matthieu SIMON
 * @version 1.0 du 14/06/05
 */
public class OpcodeSUBB extends Opcode {
	public void execute(CORE_CPU8051 cpu) throws OpcodeException {
		int a, src;
		
		if((a = decodeAddressingMode(cpu.getCurrentLine().getOperand(1))) != CORE_CPU8051.ACC)
			throw new OpcodeException(this, "Bad Addressing Mode");
		if((src = decodeAddressingMode(cpu.getCurrentLine().getOperand(2))) == Integer.MAX_VALUE)
			throw new OpcodeException(this, "Bad Addressing Mode");
		
		a = CORE_CPU8051.internalDataMem[a];
		src = CORE_CPU8051.internalDataMem[src];
		
		int i, out = 0;
		byte old_c = (byte)((CORE_CPU8051.internalDataMem[CORE_CPU8051.PSW]>>7)&1), new_c = 0;
		byte s, OV = 0;
		
		CORE_CPU8051.internalDataMem[CORE_CPU8051.PSW] &= ~0xC4; // clear C, AC et OV
		
		for(i = 0; i < 8; i++) {
			s = (byte)((byte)((a>>i)&1) - (byte)((src>>i)&1));
			if(s == -1) {
				s = 1;
				new_c = 1;
			}
			s -= old_c;
			if(s == -1) {
				s = 1;
				new_c = 1;
			}
			out |= s << i;	
			old_c = new_c;
			new_c = 0;
			
			if(i == 3 && old_c == 1) // Carry BCD
				CORE_CPU8051.internalDataMem[CORE_CPU8051.PSW] |= 0x40; // AC flag
			if(i == 6 && old_c == 1) // Overflow si pas de retenu a la fin
				OV = 1;
		}
		OV = (byte)(((OV == 1 && old_c == 0) || (OV == 0 && old_c == 1)) ? 1 : 0);
		CORE_CPU8051.internalDataMem[CORE_CPU8051.PSW] |= (old_c<<7) | (OV<<2);
		CORE_CPU8051.internalDataMem[CORE_CPU8051.ACC] = (byte)out;
		cpu.incCyclesCount(1);
	}
}