Serial Comms and Crystals

[Scampy]

The code does include DT's INT file.

I've found an indepth data sheet which states that each two way communication process should take 4ms, so why it seems that the code runs slow might of been down to the use of the wrong crystals ??

Basically connection is via a single pin. This pin is kept high by pull up resistor. To get data, the PIC needs to make the pin go low for a minimum of 18ms then hight again and waits 20-40us for the response. The sensor then sends a response by taking the pin low for 80us and then back up high for a further 80us and then sends the data, which is a 40bit stream of high pulses with a duration of 20-28us to represent a 0 or 70us for a 1. Each pulse is preceded by a low pulse of 50us, with a final 50us low at the end of the data stream.

I've seen examples using pulseIN command, with pause xxUS to trick the sensor into sending data, but don't know if interrupts could be used here ?

here's the data sheet http://www.micropik.com/PDF/dht11.pdf

[richard]

dht11/dht22
http://www.picbasic.co.uk/forum/showthread.php?t=19800

[Charlie]

You could use an HIH 4030. It outputs a voltage that you read with the ADC - as fast as you like.

[Scampy]

dht11/dht22
http://www.picbasic.co.uk/forum/showthread.php?t=19800

Thanks for the link. It states that it was for a 64mhz clock speed. Any idea what I need to change to make it run at 40 mhz ?

[richard]

this should be close

if ((tmr6 <75)||(tmr6>85))then goto badread

would become

if ((tmr6 <45)||(tmr6>55))then goto badread

and

if ((tmr6>20)&&(tmr6<80)) then     ' noise ?
           if (tmr6 >50 ) then

would become

 if ((tmr6>12)&&(tmr6<50 then     ' noise ?
           if (tmr6 >31 ) then

[Scampy]

Richard, thanks for the suggestions.

I'm in the process of editing the code (to reflect the pins I'm using and that I don't have a serial LCD), and came up with an error, presumably as I'm using 2.60 version rather than PBP 3 related to tmr6 and t6con statements. Any ideas

[richard]

pic 18F4580 has no timer6 try using tmr2 or rework the timer counts for timer3 with a 8:1 prescale

[Scampy]

Richard,

need some additional help. The following code compiled, but displayed RH 0.0 and tmr 0 on the LCD. I changed the values for badread and noise as suggested, but still have the same result. As mentioned I'm using a 10 mhz crystal with HS_ppl enabled to run the pic at 40 Mhz. Could you point me in the right direction as to what I'm doing wrong ?

; config settings 18F4580, 10mhz crystal HSPPL

ASM  
  __CONFIG    _CONFIG1H, _OSC_HSPLL_1H
  __CONFIG    _CONFIG2L, _PWRT_ON_2L  
  __CONFIG    _CONFIG2H, _WDT_ON_2H & _WDTPS_512_2H
  __CONFIG    _CONFIG3H, _PBADEN_OFF_3H
  __CONFIG    _CONFIG4L, _LVP_OFF_4L & _XINST_OFF_4L
ENDASM

DEFINE  OSC 40
ADCON1 = $0F
clear
INCLUDE "alldigital.pbp"
CMCON = 7 
TRISA = %11001111

DEFINE LCD_DREG  PORTB           ' LCD Data port
DEFINE LCD_DBIT  0               ' starting Data bit (0 or 4)
DEFINE LCD_EREG  PORTB           ' LCD Enable port
DEFINE LCD_EBIT  5               '     Enable bit  (on EasyPIC 5 LCD)
DEFINE LCD_RSREG PORTB           ' LCD Register Select port
DEFINE LCD_RSBIT 4               '     Register Select bit   (on EasyPIC 5 LCD)
DEFINE LCD_BITS  4               ' LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 4               ' number of lines on LCD
DEFINE LCD_COMMANDUS 2000        ' Command delay time in us 
DEFINE LCD_DATAUS 50             ' Data delay time in us 

ASM       
hum          = _dht+3    
tempa         = _dht+1
ENDASM 

T1CON = %00000001                               ; free-running, 1:1 prescaler

dht_data var PORTA.1
dht_dir var TRISA.1
dht var byte[5]

tempa var word EXT
bits var byte
crc   var byte
hum  var word EXT 

main:
gosub read_dht
LCDOut $FE,$94,"rh ",#hum/10,".",dec1 hum//10
pause 4000
goto main
    
read_dht:
     for bits=4 to 0 step-1 
       dht[bits]=0 
     next
    
     tmr2=0
     dht_dir=0
     dht_data=0
     pauseus 1000                   'start it up
     dht_data=1
     pauseus 30
     dht_dir=1
     pauseus 40                    'wait till middle of response pulse window
     if ( dht_data)then goto badread   'no response then  give up
     while (!dht_data)
     wend 
     t2con=6
     while ( dht_data) 
     wend 
     t2con=0
     if ((tmr2 <75)||(tmr2>85))then goto badread      ' confirm presence ?
     for  bits =39 to 0  step -1
         tmr2=0
         while (!dht_data) 
         wend 
         t2con=6
         while ( dht_data) 
         wend 
         t2con=0
         if ((tmr2>20)&&(tmr2<80)) then     ' noise ?
           if (tmr2 >50 ) then
              dht.0[bits] =  1 
           endif   
           
         else
          goto badread          ' noise ?
         endif
     next 
     crc=0 
     for bits=1 to 4         
       crc=crc+ dht[bits]
       
     next
     if crc !=  dht[0] then goto badcrc    'crc

return
  
badread:
LCDOut $FE,$94 +8,"tmr6 ",#tmr2
    for bits=4 to 0 step-1 
       dht[bits]=0 
    next
return
badcrc:
    for bits=4 to 0 step-1 
LCDOut $FE,$94 +16,hex dht[bits],"," 
    next  
return