DS1287 RTC and The internal lithuim battery?

[SphinX]

ds1287

Hi,

I have interfaced DS1287 RTC with AT89C52 (Thanks seaspac for his great help).

I read from the datasheet when VCC falls below a level of approximately 3V, the external VCC supply is switched off, and an internal lithium energy source supplies power to the RTC and the RAM memory.

and

As VCC falls below 3V typical, the RAM and timekeeper are
switched over to an internal lithium energy source. The timekeeping function maintains an accuracy of (+-)1 minute per month at +25C, regardless of the voltage input on the VCC pin.

Ok in my design the RTC is connected to VCC, i have set the RTC in the first time (setting Seconds, Minutes,....etc)

But when i remove the VCC then connect it again after while. It starts to count from the last point( when i removed the VCC)
Why that and as i know, when the VCC is removed the internal battery works to keep the time and date ?!

Please i want some explaination ?

Salam,
SphinX

 

[M!k]

ds 1287

DS1287 is obsolete and so i think you've got an old chip (look at the date code). Perhaps the battery is empty?
Take a look at this application note:
**broken link removed**

Mik

 

[Elavionic]

rtc internal battery

I don't know that exact RTC but in several RTC from Maxim or Dallas is necessary to enable the internal battery (a config bit in a register) , read carefully the datasheet to see if that's case.

 

[john_b]

dallas timekeeper ds1287 -ds12887

you can use DS1307 it,s better to you

 

[IanP]

rtc + internal battery

The battery should be in order for next 5 - 10 years ..
There are several points here:
1. DS1827 may not like the way you control the CE line. Is it operated by proper monitoring IC such sa for example DS1210?
2. On power on what code do you send to it to set it up?
I use the same code that I created some time ago for 146818 and it works without any change, like drop-in replacement.
Here is how it look like:

MOV DPTR, #000Ch
MOVX A, @DPTR ; Clear Reg. C

MOV DPTR, #000Ah
MOV A, #20h ; H3_02=0A
MOVX @DPTR, A ; 00..4,1MHz, 20..32kHz..

MOV DPTR, #000Bh
MOV A, #12h ; H3_02=2A
MOVX @DPTR, A ; 22 disables SQWE, intr..enabled

MOV DPTR, #0001h ; Set alarm int every 1 sec.
MOV A, #0C0h
MOVX @DPTR, A
INC DPTR
INC DPTR
MOVX @DPTR, A
INC DPTR
INC DPTR
MOVX @DPTR, A

 

[Nick C.]

what is a internal rtc

Speaking of NVSRAM's, I have a question about the lithium
cells that I haven't seen answered in the data sheets from
the various manufacturers.

The backup time is usually listed as 5-10 years, after
applying power for the first time (the cells come internally
disconnected until first power-up).

My question is, with a new part that has never had power applied,
will the lithium cells still self discharge over time in storage? :?

Nick