Reading and fixing Chinese scales

[BillTodd]

This is running off a remote 1.5V supply generated using a 555 and a -ve charge pump

Can't you use a spare o/p pin on the PIC instead of the 555?

and a few tens of lines of C code later...

I s C fast enough to read the clock pulses or are you using in-line assembler ? (ISTR the guy on cnczone couldn't get it to work in C)

Bill/Robin, I know you guys have both done something along these lines already, how did you force the scales into fast read mode (currently I do this by hand) and, more importantly, how did you know when they got there and weren't in some 'hold' mode?

If you look at the PIC code I posted on the CNCzone site, you'll see the sequence I used (I don't have it to hand ATM).

Essentially, I measure the data repeat rate from the scale to determine the current mode then apply pulses to change to the desired mode. The clk/data pulse sequence varies from scale to scale so I also test the data type to determine the type of scale.

Hold mode is a PITA because i can see no way to test the scale in in that Mode. In the end, I just used a reliable 'get back to normal' sequence then output the fast mode sequence blindly.

I have a one scale here that requires one extra pulse to get it to fast mode from hold, yet no way to determine the that this is a different type of scale from within the PIC. I will either have to program a special chip just for this scale or change the PIC code so it stores the sequence in EEPROM , that way I can change it from the PC program.

[edit]
Here you go:

;Zero vernier display 
Zero        movf    rxbuff+1,w
        andlw    0xDF
        xorwf    IDbyte,w    ;test correct axis 
        btfss    status,z
        return

        call    zeronorm
        btfss    Mode,Fast    ;if it was in fast mode then setfast
        return
        goto    setFast

;set zero normal mode        
ZeroNorm    call    measure    ;measure checks the clock to determine fast/slow mode
        btfss    Mode,Fflg
        goto    tstslow
pdlp        call    PlsData        ;pulse data until slow
        call    measure
        btfsc    Mode,Fflg    ;test slow        
        goto    pdlp
        call     PlsClk        ;pulse clk (zero switch)
        return

;measure the vernier reading speed (300mS slow,20mS fast)
measure        bcf    CMCON,CIS    ;switch comp to clk input
        call    synlp        ;wait for clock low >1mS
        bcf    Mode,Fflg
;if clock occurs within ~25mS then Fast flag will be set
        movlw    25
        movwf    vdata        ;borrow vdata as counter
m2lp        btfsc    CMCON,COUT
        bsf    Mode,Fflg    ;
        decfsz    vdata+3,f
        goto    m2lp    
        decfsz    vdata,f
        goto    m2lp
        return
Tstslow        call     PlsClk        ;pulse clk
        call    measure        
        btfsc    Mode,Fflg    ;test slow    
        goto    pdlp        ;if fast, pulse data until slow    
        return            ;normal zero