ORG 0000HLJMP STARTORG 0030HSTART: MOV SP. #60HST1: CLR AMLOOP: MOV P1,ACALL DELAYINC AJNB ACC.3 MLOOPSJMP STIDELAY: MOV R7,#0DLI: MOV R6, #0DJNZ R6,$DJNZ R7.DL1RETEND这段汇编语言中,JNB ACC.3 MLOOP这句话到底是怎么循环的啊,可以具体讲解一下吗,是怎么实现的