Serial Comms and Crystals

**richard** · - 24th March 2015, 21:19

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

**Scampy** · - 24th March 2015, 23:19

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 ?

Code:

; 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

**richard** · - 25th March 2015, 00:22

you did not make the changes I suggested

; 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 <45)||(tmr2>55))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>12)&&(tmr2<50)) then ' noise ?
if (tmr2 >31 ) 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

**richard** · - 25th March 2015, 00:40

if you don't have a oscilloscope or logic analyser add some more diagnostics to the program

Code:

 ; 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 badresponce 'no response then give up
 while (!dht_data)
 wend 
 t2con=6
 while ( dht_data) 
 wend 
 t2con=0
 if ((tmr2 <45)||(tmr2>55))then goto badpresence ' 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>12)&&(tmr2<50)) then ' noise ?
 if (tmr2 >31 ) 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,"tmr2 ",#tmr2
 
 next
 return
 badcrc:
 for bits=4 to 0 step-1 
 LCDOut $FE,$94 +16,hex dht[bits],"," 
pause 5000
 next 
 return
badresponse:
 LCDOut $FE,$94 +8,"nr "
 return

badpresence:
 LCDOut $FE,$94 +8,"pr",#tmr2
 return

**Scampy** · - 25th March 2015, 01:22

Originally Posted by richard

you did not make the changes I suggested

Originally Posted by Scampy

I changed the values for badread and noise as suggested, but still have the same result.

Sorry Richard, I must of confused you by posting the code with the values in the original code.

I'll take a look at your suggested code tomorrow and let you know - cheers for your help

EDIT - loaded the code as is and the LCD displays rh 0.0 nr
I assume that it's not getting a response from the sensor ? I have checked the connections and they appear correct (+ve to 5v, GND to ground, and signal to PORT A pin 1) this is connected via a header to the EasyPIC5 board with the 10K pull up resistors enabled (also tried without) I have a Hantek PC scope which I can use to test. I'm guessing I should see pin A1 going from high to low for the initial handshake between PIC and sensor ??

**richard** · - 25th March 2015, 03:08

expected dht response to start signal

**Scampy** · - 25th March 2015, 13:49

OK seems to of been a hardware issue. Replaced the sensor and now get a value on the lcd. The program is giving a reading of 870.4 - how would I turn this into a percentage

**Tabsoft** · - 25th March 2015, 16:19

Just to get a sense of the raw data collected, perhaps you can change your "main" subroutine to the follow and post the results output on the LCD?

Code:

main:
 gosub read_dht
 'LCDOut $FE,$94,"rh ",#hum/10,".",dec1 hum//10
 lcdout $FE, $94, hex2 dht(0), " ", hex2 dht(1), " ",hex2 dht(2), " ", hex2 dht(3), " ", hex2 dht(4)
 pause 4000
 goto main

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