John Payson wrote:

> [btw, in an early draft of this post, I included a routine
> to send a byte uart-style out a PIC port pin at a rate of
> one bit per three clocks as an example of something I think
> could not be done at all reasonably in C [not that the assembly
> version reads all that much better.  It didn't really fit
> my main points, but it's sorta clever so I'll put it below]

John,

After seeing only a little challenge in the comment I recoded
the routine in C. The result isn't that much of a surprise
since C's roots are that of a structured assembler. The listing
fragment that follows generates the same code as the assembler
source you posted.

Walter Banks
http://www.bytecraft.com

                                 void Payson (bits Data)
001C                                {
0005 009C    MOVWF  1C

0006 1006    BCF    PORTB,0               PORTB.0 = 0;
0007 1C1C    BTFSS  1C,0                  if(Data.0 == 0)
0008 2820    GOTO   0020h                        goto   Clr1;
0009 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set1:
000A 189C    BTFSC  1C,1                  if(Data.1 == 1)
000B 2823    GOTO   0023h                        goto   Set2;
000C 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr2:
000D 1D1C    BTFSS  1C,2                  if(Data.2 == 0)
000E 2826    GOTO   0026h                        goto   Clr3;
000F 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set3:
0010 199C    BTFSC  1C,3                  if(Data.3 == 1)
0011 2829    GOTO   0029h                        goto   Set4;
0012 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr4:
0013 1E1C    BTFSS  1C,4                  if(Data.4 == 0)
0014 282C    GOTO   002Ch                        goto   Clr5;
0015 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set5:
0016 1A9C    BTFSC  1C,5                  if(Data.5 == 1)
0017 282F    GOTO   002Fh                        goto   Set6;
0018 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr6:
0019 1F1C    BTFSS  1C,6                  if(Data.6 == 0)
001A 2832    GOTO   0032h                        goto   Clr7;
001B 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set7:
001C 0000    NOP                          NOP();
001D 1F9C    BTFSS  1C,7                  if(Data.7 == 0)
001E 1006    BCF    PORTB,0               PORTB.0 = 0;
001F 2836    GOTO   0036h                        goto    Ending;
                                  Clr1:
0020 1C9C    BTFSS  1C,1                  if(Data.1 == 0)
0021 280D    GOTO   000Dh                        goto   Clr2 ;
0022 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set2:
0023 191C    BTFSC  1C,2                  if(Data.2 == 1)
0024 2810    GOTO   0010h                        goto   Set3 ;
0025 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr3:
0026 1D9C    BTFSS  1C,3                  if(Data.3 == 0)
0027 2813    GOTO   0013h                        goto   Clr4 ;
0028 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set4:
0029 1A1C    BTFSC  1C,4                  if(Data.4 == 1)
002A 2816    GOTO   0016h                        goto   Set5 ;
002B 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr5:
002C 1E9C    BTFSS  1C,5                  if(Data.5 == 0)
002D 2819    GOTO   0019h                        goto   Clr6 ;
002E 1406    BSF    PORTB,0               PORTB.0 = 1;
                                  Set6:
002F 1B1C    BTFSC  1C,6                  if(Data.6 == 1)
0030 281C    GOTO   001Ch                        goto   Set7 ;
0031 1006    BCF    PORTB,0               PORTB.0 = 0;
                                  Clr7:
0032 0000    NOP                          NOP();
0033 1B9C    BTFSC  1C,7                  if(Data.7 == 1)
0034 1406    BSF    PORTB,0                      PORTB.0 = 1;
0035 2836    GOTO   0036h                 goto    Ending          //
Waste the extra cycle
                                  Ending:
0036 1406    BSF    PORTB,0               PORTB.0 = 1;
                                          // End of routine
0037 0008    RETURN                 }