一個(gè)從定時(shí)計(jì)數(shù)器賦初值引起的故事

程序變得非常龐大，代碼從28B猛增到169B：

C:0x0000    02009D   LJMP     C:009DC?SIDIV:C:0x0003    C2D5     CLR      F0(0xD0.5)C:0x0005    EC       MOV      A,R4C:0x0006    30E709   JNB      0xE0.7,C:0012C:0x0009    B2D5     CPL      F0(0xD0.5)C:0x000B    E4       CLR      AC:0x000C    C3       CLR      CC:0x000D    9D       SUBB     A,R5C:0x000E    FD       MOV      R5,AC:0x000F    E4       CLR      AC:0x0010    9C       SUBB     A,R4C:0x0011    FC       MOV      R4,AC:0x0012    EE       MOV      A,R6C:0x0013    30E715   JNB      0xE0.7,C:002BC:0x0016    B2D5     CPL      F0(0xD0.5)C:0x0018    E4       CLR      AC:0x0019    C3       CLR      CC:0x001A    9F       SUBB     A,R7C:0x001B    FF       MOV      R7,AC:0x001C    E4       CLR      AC:0x001D    9E       SUBB     A,R6C:0x001E    FE       MOV      R6,AC:0x001F    120039   LCALL    C?UIDIV(C:0039)C:0x0022    C3       CLR      CC:0x0023    E4       CLR      AC:0x0024    9D       SUBB     A,R5C:0x0025    FD       MOV      R5,AC:0x0026    E4       CLR      AC:0x0027    9C       SUBB     A,R4C:0x0028    FC       MOV      R4,AC:0x0029    8003     SJMP     C:002EC:0x002B    120039   LCALL    C?UIDIV(C:0039)C:0x002E    30D507   JNB      F0(0xD0.5),C:0038C:0x0031    C3       CLR      CC:0x0032    E4       CLR      AC:0x0033    9F       SUBB     A,R7C:0x0034    FF       MOV      R7,AC:0x0035    E4       CLR      AC:0x0036    9E       SUBB     A,R6C:0x0037    FE       MOV      R6,AC:0x0038    22       RET      C?UIDIV:C:0x0039    BC000B   CJNE     R4,#0x00,C:0047C:0x003C    BE0029   CJNE     R6,#0x00,C:0068C:0x003F    EF       MOV      A,R7C:0x0040    8DF0     MOV      B(0xF0),R5C:0x0042    84       DIV      ABC:0x0043    FF       MOV      R7,AC:0x0044    ADF0     MOV      R5,B(0xF0)C:0x0046    22       RET      C:0x0047    E4       CLR      AC:0x0048    CC       XCH      A,R4C:0x0049    F8       MOV      R0,AC:0x004A    75F008   MOV      B(0xF0),#0x08C:0x004D    EF       MOV      A,R7C:0x004E    2F       ADD      A,R7C:0x004F    FF       MOV      R7,AC:0x0050    EE       MOV      A,R6C:0x0051    33       RLC      AC:0x0052    FE       MOV      R6,AC:0x0053    EC       MOV      A,R4C:0x0054    33       RLC      AC:0x0055    FC       MOV      R4,AC:0x0056    EE       MOV      A,R6C:0x0057    9D       SUBB     A,R5C:0x0058    EC       MOV      A,R4C:0x0059    98       SUBB     A,R0C:0x005A    4005     JC       C:0061C:0x005C    FC       MOV      R4,AC:0x005D    EE       MOV      A,R6C:0x005E    9D       SUBB     A,R5C:0x005F    FE       MOV      R6,AC:0x0060    0F       INC      R7C:0x0061    D5F0E9   DJNZ     B(0xF0),C:004DC:0x0064    E4       CLR      AC:0x0065    CE       XCH      A,R6C:0x0066    FD       MOV      R5,AC:0x0067    22       RET      C:0x0068    ED       MOV      A,R5C:0x0069    F8       MOV      R0,AC:0x006A    F5F0     MOV      B(0xF0),AC:0x006C    EE       MOV      A,R6C:0x006D    84       DIV      ABC:0x006E    20D21C   JB       OV(0xD0.2),C:008DC:0x0071    FE       MOV      R6,AC:0x0072    ADF0     MOV      R5,B(0xF0)C:0x0074    75F008   MOV      B(0xF0),#0x08C:0x0077    EF       MOV      A,R7C:0x0078    2F       ADD      A,R7C:0x0079    FF       MOV      R7,AC:0x007A    ED       MOV      A,R5C:0x007B    33       RLC      AC:0x007C    FD       MOV      R5,AC:0x007D    4007     JC       C:0086C:0x007F    98       SUBB     A,R0C:0x0080    5006     JNC      C:0088C:0x0082    D5F0F2   DJNZ     B(0xF0),C:0077C:0x0085    22       RET      C:0x0086    C3       CLR      CC:0x0087    98       SUBB     A,R0C:0x0088    FD       MOV      R5,AC:0x0089    0F       INC      R7C:0x008A    D5F0EA   DJNZ     B(0xF0),C:0077C:0x008D    22       RET      

2: void main()
3: {
4: int i;
5: unsigned char j;
6: i=-10000;
7:
C:0x008E 7FF0 MOV R7,#B(0xF0)
C:0x0090 7ED8 MOV R6,#0xD8
8: j=i/256;
9:
C:0x0092 7C01 MOV R4,#0x01
C:0x0094 7D00 MOV R5,#0x00
C:0x0096 120003 LCALL C?SIDIV(C:0003)
C:0x0099 8F08 MOV 0x08,R7
10: while(1)
C:0x009B 80FE SJMP C:009B

就是一個(gè)signed和unsigned的區(qū)別，用的著差別這么大嗎？

通過以上的實(shí)驗(yàn)，可以得出結(jié)論:Keil編譯器非常智能，會(huì)生成最短的代碼，能夠智能判斷每個(gè)變量的使用，生成最短的代碼。同時(shí)，學(xué)習(xí)單片機(jī)的各位同仁，除非萬不得已，千萬不要用signed類型。