32.768kHz external crystal for TMR1 time base and internal 4MHz oscillator

[richard]

TMR1CS:
Timer1 Clock Source Select bit

T1CON = %00111011 ' Timer1 OSC enabled, Timer1 enabled, presc.1:8

[richard]

plus config needs to enable internal osc

 __config  _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOD_ON & _IESO_ON & _FCMEN_ON

[flotulopex]

I've modified the code according to the answers.

But with or without the 32,768kHz crystal, the LED will always blink.

As per datasheet, I have enabled LP oscillator. Why should I set the internal oscillator instead please?

Same question for T1CON.TMR1CS; why should I set this one?

' ====== FUSES ====================================================================================
' PIC 16F690
 __config  _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOD_ON & _IESO_ON & _FCMEN_ON

' ====== INTERRUPT SERVICE ROUTINE ================================================================
GOTO INIT: ' Just to place ISR at top of program
DISABLE
ISR: 'if TMR1IF is set (TMR1 has overflown)
    toggle PORTB.6 'LED
    PIR1.0 = 0 ' clear TMR1IF overflow flag
    resume
ENABLE

' ====== INITIALIZE ===============================================================================
INIT:
PAUSE 1000 'circuit settle time

' ====== DEFINES ==================================================================================
DEFINE OSC 4

' ====== REGISTERS ================================================================================
'             76543210
OPTION_REG = %10000000 ' Pull-Ups disabled
OSCCON     = %01100000 ' Internal RC set to 4Mhz
ANSEL      = %00000000 ' Analog inputs Channels 0 to 7
ANSELH     = %00000000 ' Analog inputs Channels 8 to 11
INTCON     = %11000000 ' INTerrupts CONtrol: GIE is ON, PEIE is ON 
T1CON      = %00111011 ' Timer1 OSC enabled, Timer1 enabled, presc.1:8
PIE1       = %00000001 ' Enable TMR1IF overflow flag

' ====== PROGRAM ==================================================================================
ON INTERRUPT GOTO ISR

MAIN:
    goto MAIN:
END

[richard]

As per datasheet, I have enabled LP oscillator. Why should I set the internal oscillator instead please?

if I understand correctly your intent is to use the intosc @4mhz for cpu clock and the ext osc @32khz for timer1 clk source

so to use the HFINTOSC @4mhz config= _INTRC_OSC_NOCLKOUT [no clk out assumed]
osccon= $60

Same question for T1CON.TMR1CS; why should I set this one?

to use the ext osc for timer1

you must enable the ext osc
bit 3 T1OSCEN: LP Oscillator Enable Control bit
and
select ext osc as timer clock source
bit 1 TMR1CS: Timer1 Clock Source Select bit

so t1con= %00111011 with 8:1 prescale and timer on

[richard]

the data sheet says that T1OSCEN should be enable and the user should delay for a suitable time before timer is enabled

I don't have a 16f690 handy to test with

[flotulopex]

Thanks a lot Richard,

The code hereunder works

BTW, I had to change the config settings (fuses) since you might have copied them for another PIC and generated errors while compiling. Please let me know if I should take care to change some of them.

For the test, I removed the 32,768kHz crystal while running () and the LED stops blinking which is correct.

' ====== FUSES ====================================================================================
' PIC 16F690
@ __config _INTRC_OSC_NOCLKOUT &_WDT_OFF &_PWRTE_OFF &_MCLRE_OFF &_CP_OFF &_CPD_OFF &_BOR_OFF &_IESO_OFF &_FCMEN_OFF

' ====== INTERRUPT SERVICE ROUTINE ================================================================
GOTO INIT: ' Just to place ISR at top of program
DISABLE
ISR: 'if TMR1IF is set (TMR1 has overflown)
    toggle PORTB.6 'LED
    PIR1.0 = 0 ' clear TMR1IF overflow flag
    TMR1H  = 0
    TMR1L  = 0
    resume
ENABLE

' ====== INITIALIZE ===============================================================================
INIT:
PIR1.0 = 0 ' clear TMR1IF overflow flag
TMR1H  = 0
TMR1L  = 0

' ====== DEFINES ==================================================================================
DEFINE OSC 4

' ====== REGISTERS ================================================================================
'             76543210
OPTION_REG = %10000000 ' Pull-Ups disabled
OSCCON     = %01100000 ' Internal RC set to 4Mhz
ANSEL      = %00000000 ' Analog inputs Channels 0 to 7
ANSELH     = %00000000 ' Analog inputs Channels 8 to 11
INTCON     = %11000000 ' INTerrupts CONtrol: GIE is ON, PEIE is ON 
T1CON      = %00111011 ' Timer1 OSC enabled, Timer1 enabled, presc.1:8
PIE1       = %00000001 ' Enable TMR1IF overflow flag

' ====== PROGRAM ==================================================================================
PAUSE 1000 'circuit settle time

ON INTERRUPT GOTO ISR

MAIN:
    goto MAIN:
END

[richard]

BTW, I had to change the config settings (fuses) since you might have copied them for another PIC and generated errors while compiling. Please let me know if I should take care to change some of them.

config was generated by meCONFIG for pbp3

[flotulopex]

config was generated by meCONFIG for pbp3

I have 2.6 so this may be why there is a change