----- Original Message ----- From: Henry Carl Ott To: Sent: Thursday, September 30, 1999 7:21 PM Subject: Re: I2C Realtime Clock Problem . I also rewrote the I2C routines so that the > pic never drives the SDA line high, but tristates SDA and lets the pullup > pull the the line hi. If you refer to the I2C specifications 1995 from Philips, you will see that open drain/collector is actually specified. This enables bus contentions to be detected by checking that when either line is released (ie pulled high) that it actually *goes* high ! If it is low, then another device is attempting to use the bus. If you drive high, you can potentially be shorting your +5v PIC o/p to 0v (albeit via the I2C lines of another device). Chances are the designer of the other device has kindly included some current limiting so you won't destroy either device, but what if you are communicating with another PIC driving low ....???..... The outcome is anyones guess! PIC o/ps are totem-pole arrangements, so you MUST tristate (set as inputs using TRIS reg) to ensure true I2C compatibilty. Moral of the story: Read and understand the relevant standards *before* writing your code. > At 09:49 PM 9/29/1999, you wrote: > >Hi everyone... > > > >I'm currently trying to get a PCF8583 realtime clock running and are having > >some difficulty. I use a PIC16C84 to emulate the I2C bus. There is nothing > >wrong with the I2C procedures since I also use them to access other I2C > >devices on the same bus. I want the clock to give me an interrupt every 6 > >minutes. It seems that whenever I read from the clock IC via I2C it doesn't > >accept any other commands. It just hangs!!!. Please, can you help me? Maybe > >there is something wrong with the datasheet and maybe I just missed > >something? > > > >Thanx for any help > > > >Menno J Houtman > > > carl > > -------------------------------------------------------- > Henry Carl Ott N2RVQ carlott@interport.net > http://www.interport.net/~carlott/ > -------------------------------------------------------- > You're entitled to your own opinions. > You are not entitled to your own facts. >