??? 06/22/04 10:44 Read: times Msg Score: +1 +1 Good Question |
#72926 - Real Time Clock PCF8563 Inaccuracy |
Hi Forum Members,
We have developed a product using P89C51RD2. We have used the PCF8563 as Real Time Clock. We have designed the PCB by refering to the AppNote of Philips mentioning the layout of crystal. We have taken care to see that there are NO digital signals going close to the crystal circuit. We have given a separate ground track from the source to the VSS pin of RTC. We have used a 32768 Hz (100ppm) crystal. We have connected a 5-25pF trimmer between Pin 1 and GND. We have given power through diodes from 2 sources: 1) Lithium Battery 3V, and , 2) Vcc(+5V) We tested the timings by comparing the timings with a digital clock. The digital clock is working OK, we have compared the timings of this digital clock with the local railway timings, FM-Radio, and the telephone services which give the Indian-Standard-Time (IST). We found that when the product is given the mains supply its runs slow by about 1 minute/hour. But if it is kept OFF, it works accurately. For testing the accuracy of the RTC we did the following tests: Parameter1: When the Mains Power is ON, the RTC gets a supply of +5V, but when power is OFF, it gets a supply of +3V. Is Power supply voltage messing the accuracy of the RTC? Test1: Removed the Diode coming from Vcc. So RTC gets +3V (from Battery) when power is ON or OFF. Result1: With the Mains Power ON, Clock runs slow by about 1 minute/hour. When Power is OFF, it works accurately. Conclusion1: The Power Supply voltage is not affecting the accuracy of the RTC (atleast in this test). Parameter2: We are reading the RTC at about "4-5 times per minute". Is reading the RTC effecting the RTC accuracy? Test2: Placed a cut-jumper on SCL pin. Placed the jumper when taking the reading then removing the jumper. Result2: When Power is ON, Clock runs slow by "2 minutes/day" but runs accurately when kept OFF. Conclusion2: The accuracy is improved when the SCL pin is kept Open; But even this (improved?) accuracy is not acceptable. 1. Can you give me any suggestions for further tests to be performed? 2. Can you point out any mistake or suggestions that I must take care when performing the above tests ? 3. Can you suggest any other IIC based RTC, based on your experience ? Please Note: The Readings were taken after a gap of minumum 8 hours to 48 hours, during each ON cycle and then the OFF cycle. Then estimating the accuracy for per hour based on atleast 2 results each from ON cycle and the OFF cycle. Can anybody give me link or email address of philips technical support. I had been trying for the last 4 hours on their website, and am unable to do so, its damn tooooo slow, and everytime tries to connect to the philips site. whereas on this (8052) forum, I have posted this within a few minutes (thats the sucess of this forum). Thanking you all, With best regards from, Mr. Kiran V. Sutar. |
Topic | Author | Date |
Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy | 01/01/70 00:00 | |
RE: Real Time Clock PCF8563 Inaccuracy![]() | 01/01/70 00:00 |