Making a timer, 32.768kHz+555+DT_INT. Good idea?

[financecatalyst]

Are you saying that you have two 32768 crystals?
The CPU will be running at 8192 hz (FOSC/4).

You might as well run the timer off the main clock then, (saves the power used by the timer1 oscillator), and gives the same accuracy.
T1CON = 1
Reload TMR1H with $11100000, and definitely put it First in the handler.

And change the LCD timing because PBP still thinks it's running at 4mhz.

DEFINE LCD_COMMANDUS 17
DEFINE LCD_DATAUS 1

With recommended settings above i.e. TMR1H with %11100000 can someone please help me understand how many seconds or minutes the clock will be out after a month or an year because it gives me 1.00069 Hz frequency for Timer1

[Darrel Taylor]

That would gain about 2.5 seconds per hour, which is not good.

Have you set LP oscillator mode in your configs?
Since it worked for you at 4mhz, it's probably set to XT and over driving the crystal.

How are you measuring that frequency?
Is it a high quality frequency counter?
Accurate measurements of low frequencies can be difficult, with large errors.

[financecatalyst]

That would gain about 2.5 seconds per hour, which is not good.

Have you set LP oscillator mode in your configs?
Since it worked for you at 4mhz, it's probably set to XT and over driving the crystal.

How are you measuring that frequency?
Is it a high quality frequency counter?
Accurate measurements of low frequencies can be difficult, with large errors.

Yes, I change it to LP when driving it with 32 kHz and your advised process to run timer 1 from internal clock (loading TMR1H=%11100000) & XT when 4MHz (with 32kHz attached 4 TMR1).

For frequency, unfortunately I am not equipped with those luxuries, I am just using an Timer Calculator I found in the Forum only. Screenshot attached.

[financecatalyst]

Even with loading 32768 into TMR1, the calculator shows the interrupts 1.00027 Hz.
This is just to seek clarification, it is unlikely that I will be able to use 4MHz for OSC & 32kHz for TMR1.

[Darrel Taylor]

That calculator is wrong.

Here's the way it works ...
The main OSC is running at 32768 hz.
The CPU is running a 8192 hz (32768 / 4).

Timer1 is loaded with the highbyte of 57344 and will overflow at 65536.
65536 - 57344 = 8192

So the timer overflows exactly 1.0000 seconds every time (depending on the crystal tolerance).

[financecatalyst]

That calculator is wrong.

Here's the way it works ...
The main OSC is running at 32768 hz.
The CPU is running a 8192 hz (32768 / 4).

Timer1 is loaded with the highbyte of 57344 and will overflow at 65536.
65536 - 57344 = 8192

So the timer overflows exactly 1.0000 seconds every time (depending on the crystal tolerance).

OK, I am now running everything as advised. I synchronised the time with my phone last night. Today appx after 12 Hrs, the phone is appx 6 seconds ahead than the clock. What could be the possible problem?

[Dave]

Financecatalyst, I would first check that the crystal is indeed operating at the proper frequency... (Frequency counter)

Dave Purola,
N8NTA