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06/01/2009 #1


Cristal externo y oscilador interno para atmega16
Hola haber si me pueden ayudar, en la universidad me han dejando un proyecto en el cual necesito, tener como variable de tiempo segundos, exactos porque es un proceso de medida, entonces diseñe el sistema en base del atmega16, entonces para obtener los segundos utilice el timer dos con la entrada de cristal de 32768hz cargando el prescaler con 128 obtengo un segundo, y para el resto de programa lo configure para un el oscilador de 8mhz, entonces ahi va mi gran duda, no se si se puede hacere esto, de trabajar con un cristal externo para el timer2 y y lo demas con oscilador interno, y si hay como tengo un gran inconveniente al quemar el micro nose si en el programador debo configurar eso... trabajo con el programador progisp, bueno y si no hay como trabajar con las dos fuentes de oscilacion simultaneas, que puedo hacer para obtener el segundo exacto y trabajar con lo demas de programa.

Ojala me haya hecho entender, y ojala me puedan ayudar

De ante mano gracias
06/01/2009 #2
Moderador

Avatar de Chico3001

Si puedes trabajar con ambos osciladores... solo coloca el cristal en los pines TOSC1 y TOSC2 y configura el bit ASSR:AS2 a 1
07/01/2009 #3


listo pero al colocarlo en esos pines el cristal debo configurar la interrupcion 2 y eso ya lo hice pero no funciona y no se que mas debo hacer..... o a su vez otra manera de gerar un segundo

aqui anexo el programa.

$crystal = 8000000

Config Timer0 = Counter , Edge = Falling
Config Timer1 = Pwm , Pwm = 10 , Compare A Pwm = Clear Up , Prescale = 1
Config Timer2 = Timer , Async = On , Prescale = 128

Config Portb = Input
Portb = 255
Config Portd.2 = Input
Set Portd.2

'Config Kbd = Porta , Delay = 100

Enable Interrupts
On Timer2 Segundo
Enable Timer2



Tcnt0 = 0

Dim Revoluciones As Byte
Dim Tempo As Byte
'Dim Minuto As Byte
Dim Setpoint As Byte
Dim Teclado As Byte
Dim Seguro As Byte
Dim Real As Byte
Dim Vmax As Byte
Dim Vmin As Byte
Dim Valor As Word
Valor = 511
Vmax = 60
Vmin = 5
Cursor Off

Start Counter0

Inicio:
'Enable Interrupts
Cls
Locate 1 , 1
Lcd "Medidor de flujo"
Waitms 200

Do

If Portb.1 = 0 Then Goto Set_point
If Real < 0 Then
If Valor = 1 Then
Cls
Home Up
Lcd "IMPOSIBLE COMPENSAR"
Locate 2 , 1
Lcd "VELOCIDAD MAXIMA"
End If
Valor = Valor - 1
End If

If Real > 0 Then
If Valor = 1023 Then
Cls
Home Up
Lcd "SISTEMA DETENIDO"
Locate 2 , 1
Lcd "VELOCIDAD MINIMA"
End If
Valor = Valor + 1
End If

Pwm1a = Valor
Locate 2 , 1
Lcd "Actual:"
Locate 2 , 8
Lcd Revoluciones ; " RPS"
Loop
End 'end program

Segundo:
Revoluciones = Tcnt0
'Minuto = Revoluciones * 60
Tcnt0 = 0
Return
07/01/2009 #4
Moderador

Avatar de Chico3001

Que raro lenguaje... no lo conozco es C ?

Viendo la pagina 131 del manual hay un procedimiento para tener en cuenta a la hora de configurar el TIMER 2 con un cristal externo

When Timer/Counter2 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2, and TCCR2 might be corrupted. A
safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2 and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2, and TCCR2.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and TCR2UB.
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
Tambien hay ciertas advertencias.... verifica que las tomes en cuenta

• The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external
clock to the TOSC1 pin may result in incorrect Timer/Counter2 operation. The CPU main
clock frequency must be more than four times the Oscillator frequency.
• When writing to one of the registers TCNT2, OCR2, or TCCR2, the value is transferred to a
temporary register, and latched after two positive edges on TOSC1. The user should not
write a new value before the contents of the temporary register have been transferred to its
destination. Each of the three mentioned registers have their individual temporary register,
which means for example that writing to TCNT2 does not disturb an OCR2 write in progress.
To detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented.
• When entering Power-save or Extended Standby mode after having written to TCNT2,
OCR2, or TCCR2, the user must wait until the written register has been updated if
Timer/Counter2 is used to wake up the device. Otherwise, the MCU will enter sleep mode
before the changes are effective. This is particularly important if the Output Compare2
interrupt is used to wake up the device, since the output compare function is disabled during
writing to OCR2 or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode
before the OCR2UB bit returns to zero, the device will never receive a compare match
interrupt, and the MCU will not wake up.
• If Timer/Counter2 is used to wake the device up from Power-save or Extended Standby
mode, precautions must be taken if the user wants to re-enter one of these modes: The
interrupt logic needs one TOSC1 cycle to be reset. If the time between wake-up and re-
entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering Power-
save or Extended Standby mode is sufficient, the following algorithm can be used to ensure
that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2, TCNT2, or OCR2.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or Extended Standby mode.
• When the asynchronous operation is selected, the 32.768 kHz Oscillator for Timer/Counter2
is always running, except in Power-down and Standby modes. After a Power-up Reset or
wake-up from Power-down or Standby mode, the user should be aware of the fact that this
Oscillator might take as long as one second to stabilize. The user is advised to wait for at
least one second before using Timer/Counter2 after power-up or wake-up from Power-down
or Standby mode. The contents of all Timer/Counter2 Registers must be considered lost
after a wake-up from Power-down or Standby mode due to unstable clock signal upon start-
up, no matter whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
• Description of wake up from Power-save or Extended Standby mode when the timer is
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
cycles, it executes the interrupt routine, and resumes execution from the instruction
following SLEEP.
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an
incorrect result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2
must be done through a register synchronized to the internal I/O clock domain.
Synchronization takes place for every rising TOSC1 edge. When waking up from Power-
save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will read as the previous
value (before entering sleep) until the next rising TOSC1 edge. The phase of the TOSC
clock after waking up from Power-save mode is essentially unpredictable, as it depends on
the wake-up time. The recommended procedure for reading TCNT2 is thus as follows:

1. Write any value to either of the registers OCR2 or TCCR2.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
• During asynchronous operation, the synchronization of the Interrupt Flags for the
asynchronous timer takes three processor cycles plus one timer cycle. The timer is therefore
advanced by at least one before the processor can read the timer value causing the setting
of the Interrupt Flag. The output compare pin is changed on the timer clock and is not
synchronized to the processor clock.
07/01/2009 #5


gracias amigo ya lo pude solucionar y si es lenguaje C , he problema a radicado que bascom tiene problemas para llegar a ciertos registros del micro al programarlo, y nada esa parte me toco programarla en assembler y se soluciono el problema, te agradezco por el tiempo prestado
24/05/2009 #6


dielan dijo:
gracias amigo ya lo pude solucionar y si es lenguaje C , he problema a radicado que bascom tiene problemas para llegar a ciertos registros del micro al programarlo, y nada esa parte me toco programarla en assembler y se soluciono el problema, te agradezco por el tiempo prestado
Hola haber si me pueden ayudar con un problema que tengo en tratar de variar la señal pwm del atmega16 el codigo que he hecho es el siguiente:

$regfile = "m16def.dat"
$crystal = 8000000

Ddrd.1 = 1
Portd.1 = 0
Ddrd.5 = 1
Portd.5 = 0
Config Porta.0 = Input
Config Porta.1 = Input
Set Porta.0
Set Porta.1
Dim Frec As Byte
Dim Bandera As Bit , W As Word
Frec = 128
Btn_subir Alias Porta.0
Btn_bajar Alias Porta.1
Aviso1 Alias Portd.1
Config Timer1 = Pwm , Pwm = 8 , Compare A Pwm = Clear Up , Prescale = 1024

Inicio:
Reset Aviso1
Reset Pwm1a
Do
W = Timer1
Pwm1a = Frec
If Btn_subir = 1 Then
Goto Subir
End If
If Btn_bajar = 1 Then
Goto Bajar
End If
Bandera = 0
Loop

Bajar:
If Frec < 1 Then
Goto Aviso
End If
If Bandera = 1 Then
Goto Inicio
End If
Set Aviso1
Bandera = 1
Frec = Frec - 5
Goto Inicio

Subir:
If Frec > 254 Then
Goto Aviso
End If
If Bandera = 1 Then
Goto Inicio
End If
Set Aviso1
Bandera = 1
Frec = Frec + 5
Goto Inicio

Aviso:
Set Aviso1

Goto Inicio

End

de antemano muchas gracias por su colaboración.....
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