Which RTC to use?

[mikesmixes777]

I am building a data logger using a PIC18LF252 that shall interface with an ethernet controller (EN28J60). Guess I overlooked the Date/Time stamp of the logged data and now need to add a RTC to my circuit.

I am using 3xA/D inputs, 1x D output, the 3-wire SPI for the ENC28J60,
RX-TX for RS232 and ICSP pins for ICD2 programmer.
Crystals: PIC18LF252@20MHz and ENC28J60@25MHz

Any ideas for the RTC chip?

Thanks
Mike

 

[ericgibbs]

hi,
This type is an option.

https://uk.farnell.com/jsp/search/browse.jsp?N=500004+1000010&Ntk=gensearch_001&Ntt=DS1307&Ntx=

 

[mikesmixes777]

Thanks....
The PIC being used only has one i2c / SPI interface and i'm using that for the ethernet controller. Is there another way to add a RTC to my existing circuit?
Do they all use i2c?

 

[Pommie]

Have you considered putting a watch crystal on timer1/3 oscillator pins and implementing a 1 second interrupt.

Mike.

 

[Pommie]

P.S. if you can't afford another interrupt source then you can poll it as it will only change once per second.

Mike.

 

[mikesmixes777]

That seems an interesting and probably the best way of doing it. I could generate some code to keep track of the date and time and save it into memory.

As far as interupts are concerned I have not got that far yet so I'm not sure what interupts are going to be used. I know the Ethernet side of the circuit will use an interupt at the least.

Could I not possible collect the date and time from the network? This will only be wise if the circuit is continuosly on the network and if the PC's date/time is correct.

 

[UTMonkey]

If there was an available NTP server available you could.

 

[ericgibbs]

If you have spare port pins, you could write a low level I2C routine for the RTC.

 

[Pommie]

If you have spare port pins, you could write a low level I2C routine for the RTC.

Thinking about it, that is probably the best option. My suggestion of using timer1/3 has the disadvantage that it needs resetting whenever power is cut. Futurelec do a nice little RTC module that may get you up and running and only $7.

Mike.

 

[ericgibbs]

hi,
As quick fix guide, I have compiled a Basic Low Level, I2C routine in Oshonsoft, the attached [18F252] asm file is well commented.

EDIT:
Do you need the Header details for this asm file.?

 

[mikesmixes777]

Im sort of a beginner to all this pic programming... would adding a crystal to timer1/3 be able to serve the purpose of a RTC without compramising any other issues, bare in mind i am connecting to a ENC28J60 and implemeting the TCP/IP stack on the pic to handle the network interface....(i guess this is going to use alot of resources?)

edit: sorry didnt see the reply posts.....just busy thinking thru erics routine...

 

[mikesmixes777]

Please could you give the header files for asm.

I see that PORTC 3 and 4 are *currently used for the SPI as a default. Can i just change it to two free ports say PORTB?
Does the code need any adjusting for inserting it into C18?

Thansk for your help....I appreciate it.

 

[Pommie]

the attached [18F252] asm file is well commented.

You needed a VERY big smiley after that comment.

Mike.

 

[mikesmixes777]

It is serious giberish to me...but that is no-one's fault except mine....

 

[ericgibbs]

hi,
I dont do 'C'...

Hi Mike,
I should have said " the modules are commented"...

Shouldn't you be in bed...

I cant help the OP with a 'C' conversion, I am wrinkly using asm!!!

 

[eng1]

The PIC being used only has one i2c / SPI interface and i'm using that for the ethernet controller.

What's wrong about connecting both the controller and the RTC to the SPI 'bus'?

 

[Pommie]

Hi Mike,
Shouldn't you be in bed...

Yes.

I cant help the OP with a 'C' conversion, I am wrinkly using asm!!!

Can you beat 49? I spent most of my working life writing asm. Only recently looked at C.

Mike.

 

[ericgibbs]

Yes.


Can you beat 49? I spent most of my working life writing asm. Only recently looked at C.

Mike.

Hi Mike,
Yes I can beat 49 with a good lead, I am 75 years old, well past my sell by date.

PS: spent most of my early years writing in machine code.!!!

PPS: going even further back I used enter each bit of the byte with its own switch and then press the accept key.
Entering the program Byte by byte.

 

[mikesmixes777]

What's wrong about connecting both the controller and the RTC to the SPI 'bus'?

Can this be done?

 

[blueroomelectronics]

Run the master crystal at 9.8304MHz.