I2C issues

[towlerg]

I'm guessing that you don't have scope or logic analyzer to actually see whats going on, I think thats the only way you're going to fix this. In this case I suspect a scope would be more helpful (USB from eBay £50 ish - for this you don't need lots of bandwidth) and as they are so cheap, Salea knock off (eBay £6). And before the winers start, a) Salea don't sell them any more and b) if you base your software on a reference design you shouldn't be surprised if people use alternate hardware.

George

[richard]

it works for me pbp3 pic16f1825 // ds1307 // pcf8574a either your code is wrong or your not connecting things properly

tested at 8mz an 32mhz the pcf8574a has no problem

                            
#CONFIG
   __config _CONFIG1, _WDTE_ON    & _FOSC_INTOSC   &_MCLRE_ON    &_PWRTE_ON 
   __config _CONFIG2,              _LVP_OFF   & _PLLEN_ON
#ENDCONFIG
         DEFINE OSC 32
         
            pkt var byte[11]
          MONTH VAR pkt[5]
          DATE  VAR pkt[4]
          HOUR  VAR pkt[2]
          MINS  VAR pkt[1]
          DOW VAR pkt[3]
          YEAR VAR pkt[6]
           SEC VAR pkt[0]
           cnt var byte

  
     osccon=$70    '8 MHz or 32mhz
         anselA=0        'dig i/o 
         ANSELC=0
      TRISC= 111111
       TRISA= 111110
       
   
     SDA         VAR PORTc.4       ; I2C Data pin
     SCL         VAR PORTc.3     ; I2C Clock Pin
pcf_Addr CON $78
rtc_Addr CON $d0       
      
       i2cwrite  sda,scl,rtc_Addr,0,[$80,$14,$11,3,$14,1,$14]  'SANE TIME AND DATE  
        i2cwrite  sda,scl,rtc_Addr,0,[$80]    'FORCE START IF REQ
        i2cwrite  sda,scl,rtc_Addr,0,[0]
 
  main:
  pause 2000
  i2cREAD  sda,scl,rtc_Addr,0,[str pkt \7 ]
  serout2 porta.0,84 ,[HEX HOUR,":", HEX2 MINS, ":",HEX2 sec, " - ", HEX DATE,"/", HEX MONTH  ,13,10]
  i2cwrite  sda,scl,pcf_Addr,0,[cnt]
  cnt=cnt+1
 goto main

[Amoque]

In preparation for providing a drawing, I stripped off the board the battery holder, socket, and crystal from the standalone 1307 I tried earlier (they were not wired, but were cluttering the board), then began commenting out the unneeded code to post the minimal circuitry and programming that demonstrated the problem. Somewhere along the way... it works as intended now.

You may recall that the last thread on this issue ended with my determination that it was some undiagnosed power issue related to backup battery voltage; I was not able to isolate the issue. Once again this is the case.

I am tempted to write it off as a bad soldier joint or poor connection; it hurts my pride to admit such - I was a hearing aid technician for 20 years and close tolerance work was my bread and butter; yet, I cannot think of any other cause or issue that might manifest itself in so frustrating a way.

I am looking now for a new DSO and I am convinced to get one with a logic analyzer. Issues like this are so demotivating...

Thank you all for your suggestions and your effort and advice, I appreciate it very much.