Quick thoughts: DT Ints with encoders

[kevlar129bp]

Hey Hendrik,

I'll take a glance at the parts you mentioned. Kinda cool you mentioned the uarts. Maybe you can answer a lingering question for me... In the example of the six "slaves" reporting to the "master"... If I send HSEROUT from the slaves, what would be the protocol for receiving at the master? Would I use SERIN2? What mode? Etc, etc?

That question has driven me nuts for some time!

I'm thinking 20 Mhz on the slaves and 40 Mhz on the master.

What are your thoughts?

Thanks again,

Chris

[HenrikOlsson]

Hi Chris,
There are varoius ways to do it. You could for example have two wires between each slave and the master PIC. The master signals one slave at a time to to send the current position, and receives it with SERIN or SERIN2. When all 6 slaves are polled it sends the data to the master. The USART sends the data "true" so the master would need to receive it "true".

Another approach is to implement a RS485 network.

/Henrik.

[kevlar129bp]

I'll work on a bit of code and we'll see where it takes us...

I'll keep you posted.

Thanks,

Chris

[kevlar129bp]

Here's what I've got so far... for the "slave" pics anyhow.

Critiques are definitely welcome!

16F688 w/20Mhz

INCLUDE "DT_INTS-14-MOD.bas"
INCLUDE "ReEnterPBP.bas"

'Clock setup
    Define OSC 20
'Pin setups
    ANSEL = %00000000       'No analog input
    TRISA = %00000111       'PortA: TRISA = %00XXXXXX
    TRISC = %00000000       'PortC: TRISC = %00XXXXXX
'Usart setups
    DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
    DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
    DEFINE HSER_CLROERR 1 ' Clear overflow automatically
    DEFINE HSER_SPBRG 86  ' 57600 Baud @ SPBRGH = 0
    BAUDCTL.3 = 1         ' Enable 16 bit baudrate generator
'----------------------------------------------------------------------------

MaxCount con 21600
BtnZeroCount var PORTA.0
APin var PORTA.1
BPin var PORTA.2
AOld var byte
BOld var byte
CurCount var word

ASM
INT_LIST  macro    ; IntSource,  Label,  Type, ResetFlag?
        INT_Handler   RAC_INT,  _ABInt,   PBP,  yes
    endm
    INT_CREATE           ; Creates the interrupt processor

    INT_ENABLE  RAC_INT  ; Enable RA change interrupt
ENDASM

curcount = 0

Start:

if btnzerocount = 0 then    'btnzerocount (A.0) has pullup res
    curcount = 0
endif

aold = apin
bold = bpin

hserout ["$", dec5 curcount]

goto start

ABInt:

'\\\ A caused the interrupt ///
IF apin != aold THEN                       'APin IS NOT equal to AOld
    IF apin != bpin THEN                   'If A and B are different,
        GOTO CW                                 'it was clockwise rotation
    ELSE                                   'Otherwise,
        GOTO CCW                                'it was counter-clockwise rotation
    ENDIF
ENDIF

'\\\ B caused the interrupt ///
IF Bpin != Bold THEN                       'BPin IS NOT equal to BOld
    IF apin == bpin THEN                   'If A and B are the same,
        GOTO CW                                 'it was clockwise rotation
    ELSE                                   'Otherwise,
        GOTO CCW                                'it was counter-clockwise rotation
    ENDIF
ENDIF

CW:                 ' -1
if curcount > 0 then
    curcount = curcount -1
else
    curcount = MaxCount
endif
@ INT_RETURN

CCW:                ' +1
if curcount < maxcount then
    curcount = curcount +1
else
    curcount = 0
endif
@ INT_RETURN

Thanks again guys,
Chris

[HenrikOlsson]

Hi,
I'd move the aold=apin, bold=bpin to the ISR. If kept in the main routine it's possible that a new interrupt occurs, for example, right between those two lines which will mess with your count - I think.

[kevlar129bp]

Thanks Henrik,

Thanks for the heads up. I see your point there. Otherwise, do you think I've got viable code?

Thanks again,
Chris

[HenrikOlsson]

Hi,
Yes, it look OK to me, the quadrature decoding seems to be correct but I'm sure someone around here knows of a faster/slicker way of doing it. (I'm not saying your way is slow).

Are you sending directly to a VB program for testing or are you sending to a terminal program or something like that? If a terminal program I'd put Pause 100 or whatever in the mainloop and add a CR to the end of the "message". If you're sending to a VB program, you could send the high and low byte of the counter and put them together in the PC.

If the encoders have Index-channel you could use that to zero the counter, at startup you move each joint of the arm thru "center" and it automatically zeros.

/Henrik.