SQR:     LD        20H,[1AH]                    ;取被开方数
            LD        22H,2[1AH]
           NORML   20H,26H                       ;规格化,移位次数放在26H单元
           JE          SQR3                           ;?为什么在这里跳转?什么和什么相等?
           CMPB     26H,#16                      ;移位次数和16进行比较
           JLE        SQR1                           ;为什么小于等于就跳转
           LD         24H,#0FFH                   ;下面两句表示什么意思 
           SJMP      SQR2
SQR1:  
           SHRB      26H,#1                       ;这两句又表示什么?
           LD          24H,#OFFFFH
           SHR        24H,26H
SQR2:
           LD          20H,[1AH]                   ;取被开方数
           LD          22H,2[1AH]
           CMP        22H,24H                      ;24H中为上次计算结果Xn
           JC           SQR3                          ;为什么这样比较就可以?
           DIVU       20H,24H                      ;a/Xn
           CMP        20H,24H                      ;判断结果是否相等
           JC           SQR3                          ;大于等于跳转?
           CLR         26H                            ;清移位次数
           ADD        24H,20H                     ;Xn+a/Xn
           ADDC      26H,0                         ;干吗还要加上进位位?
           SHRL       24H,#1                       ;除以2,得到1/2(Xn+a/Xn)
           SJMP       SQR2
SQR3:
           RET     

非常感谢!