Watchdoc timer connecting and setting prescaler

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Watchdoc timer connecting and setting prescaler

Postby CeesD » Mon Mar 09, 2015 4:20 pm

I have read as much as possible the topics on watchdog timer. But I do not find explanation on how to make longer watchdog time's (e.g. approx. 1 second instead of 18 msec).
What I am looking for is:
- which c-code to add in the start of a Flowcode program to 'connect' the prescaler to the watchdog timer, and
- which c-code to add there also a prescaling number, e.g. 56 (to get approximately a 1 second watchdog timespan).

I hope someone can help me in this.

Note: at the moment in the start of the Flowcode program we added e.g. the c-code " osccon = 0x60; " to use a 4 MHz oscillator (but we want to go to 32 kHz to minimize current consumption).

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Re: Watchdoc timer connecting and setting prescaler

Postby CeesD » Mon Mar 09, 2015 5:29 pm

I mentioned the word 'prescaler', but now I think it should be 'postscaler'. Could be simpler?

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Re: Watchdoc timer connecting and setting prescaler

Postby Benj » Tue Mar 10, 2015 3:37 pm

Hello,

What chip are you using and what is the clock speed? This will dictate how long you can set the watchdog timeout to last for.
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Re: Watchdoc timer connecting and setting prescaler

Postby CeesD » Wed Mar 11, 2015 4:37 pm

I am using a PIC12F683.
I want to use it at 32 kHz with external crystal oscillator.

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Re: Watchdoc timer connecting and setting prescaler

Postby Benj » Wed Mar 11, 2015 6:31 pm

Hello,

Ok that's great thanks. The Watchdog prescaler is shared with the Timer 0 so you won't be able to use timer 0 in your program.

Also the timer is linked to the 31KHz internal clock and so will not be effected by your clock speed.

Here is a C code you can insert using a C code icon at the start of your program.

Code: Select all

option_reg = option_reg | 0b00001111;     //Configure watchdog to 1:128 Postscaler
wdtcon = 0b00000111;    //Configure watchdog 1:256 Prescaler, Software Watchdog enabled


This should give you a watchdog window of (1 / (31000 / 128 / 256)) = 1.057 seconds

If you look at the datasheet then it describes the values you can use for the option_reg and wdtcon registers so you can work out what value to use to get the window you require.
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Re: Watchdoc timer connecting and setting prescaler

Postby CeesD » Wed Mar 18, 2015 5:08 pm

Thanks for your help. I think I understand it.

I want to attach an external standard 32kHz crystal oscillator signal to pin 2 (pin 3 not used). What must I add more to the program to get the 12F683 using this external clock signal?

With project build option I can already specify the 32768 frequency.

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Re: Watchdoc timer connecting and setting prescaler

Postby CeesD » Tue Mar 31, 2015 1:31 pm

The watchdog timer is now effectively 1 second. Thanks for your help.
I learned however that this does not affect overall processing time compared to the default approx. 18 msec watchdog timer.

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Re: Watchdoc timer connecting and setting prescaler

Postby amarsingh12 » Tue Sep 22, 2015 8:32 am

I am using the same code at the begining of my program.. and it is not working.. I am also attaching the flowcode file that I am building... please assist..

option_reg = option_reg | 0b00001111; //Configure watchdog to 1:128 Postscaler
wdtcon = 0b00000111; //Configure watchdog 1:256 Prescaler, Software Watchdog enabled

I am also trying to setup a 1 second WDT

Is there some thing that I am missing here.. i am just trying to make sure that the Pic reset's if the program get stuck.
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Re: Watchdoc timer connecting and setting prescaler

Postby amarsingh12 » Wed Sep 23, 2015 9:34 pm

It worked.. sorry... the clear Watch dog had to be used in every macros.. I was using it only in the main function... thanks guys for this awesome Forum
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Re: Watchdoc timer connecting and setting prescaler

Postby achillis1 » Fri Oct 30, 2015 9:23 pm

Hello,

I have pic 16F877A and I want to set the WDT to be around 1 second. Based on the data sheet details I post below what is the longest time for WDT?
The crystal is the default one 19Mhz




By the way , why do we put 0b at the beginning of the C code? "0b00000111"

2. The option_reg register I can spot on the datasheet, what about wdtcon? What is this , is a register?

3.
It worked.. sorry... the clear Watch dog had to be used in every macros.. I was using it only in the main function...


What does this user mean? Is there an option I should use for WDT in flowcode?


Thank you,

Best Regards,

Andreas Achilleos
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Re: Watchdoc timer connecting and setting prescaler

Postby medelec35 » Fri Oct 30, 2015 11:33 pm

Hi,
achillis1 wrote: have pic 16F877A and I want to set the WDT to be around 1 second. Based on the data sheet details I post below what is the longest time for WDT?
The crystal is the default one 19Mhz

The watchdog time out is totally independent of clock speed.
Timeout will be exactly the same period if using 4MHz or 64MHz clock rate.
If you take 18ms for the normal timeout (18ms is approx as actual time depends on supply voltage, temperature etc) = (1:1), then
1:2 = 18ms*2 =36ms
So maximum
= 1:128 = 18ms*128 = 2.3 seconds

achillis1 wrote:By the way , why do we put 0b at the beginning of the C code? "0b00000111"

0b is just stating that the value is binary format.
Just like 0x means the value will be in hex format e.g. 0xF8 = F8 hex.

achillis1 wrote:The option_reg register I can spot on the datasheet, what about wdtcon? What is this , is a register?

Yes but not on 16F877A
Its used on the newer devices like 16F18xx range and is used to increase watchdog timeout even longer.
For example 256 seconds.

achillis1 wrote:What does this user mean? Is there an option I should use for WDT in flowcode?

If watchdog timer setting are left as a default value then hardware will start then after 18ms will keep restarting
When you need to do to prevent this is place a C code block with

Code: Select all

MX_CLEAR_WATCHDOG;
in strategic places.
They need to be placed before 18ms has elapsed after the previous

Code: Select all

MX_CLEAR_WATCHDOG;
has prevent watchdog timer from timing out.
Another thing Flowcode allows you to do is to enable Auto clear Watchdog within Build, Project options.
What Auto clear Watchdog does is automatically places a MX_CLEAR_WATCHDOG;whenever a delay or a component containing a delay is used.
For example RS232, LCD etc.

The purpose of the watchdog timer being enabled is to reset the microelectronic if a bug or interference causes the it to get stuck in a loop.
One thing that must not be does is place a clear watchdog command within an interrupt.

Martin
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Re: Watchdoc timer connecting and setting prescaler

Postby achillis1 » Sun Nov 01, 2015 10:28 am

Hello Martin,

Always glad when you reply a post! :D

1. So, I will just use the option_reg only without the wdtcon.
2. In order to use the "option_reg = option_reg | 0b00001111; //Configure watchdog to 1:128 Postscaler" code, it is prerequisite that I enable WDT within project options, yes?
a. If I do that in order to have 2.3 seconds of delay; then if I have a RS232 component , WDT will be disabled and routine will loop until a character is received in RS232?


Thank you,

Best Regards,

Andreas Achilleos

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Re: Watchdoc timer connecting and setting prescaler

Postby medelec35 » Sun Nov 01, 2015 6:33 pm

Hi Andreas,
achillis1 wrote:Always glad when you reply a post!

Thank you, always happy to post :)
achillis1 wrote:1. So, I will just use the option_reg only without the wdtcon.

Yes that's correct.
To confirm you can always set a register value e.g

Code: Select all

wdtcon=0b1101;

You can make up the value at this stage.
Then compile and if register is not available (or misspelt) then you will just get an error.


achillis1 wrote:In order to use the "option_reg = option_reg | 0b00001111; //Configure watchdog to 1:128 Postscaler" code, it is prerequisite that I enable WDT within project options, yes?

Yes you will need to enable within configure settings and I would recommend to enable Auto Clear Watchdog on the general tab.
achillis1 wrote:If I do that in order to have 2.3 seconds of delay; then if I have a RS232 component , WDT will be disabled and routine will loop until a character is received in RS232?

No not true when WDT is enabled, watchdog timer is constantly counting up no matter what.
If the count is not reset with a clear command then as soon a maximum count is reached then hardware will reboot.
The MX_CLEAR_WATCHDOG; command and using RS232 components should each reset the WatchDog Timer to prevent hardware rebooting.

Martin
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Re: Watchdoc timer connecting and setting prescaler

Postby achillis1 » Tue Nov 03, 2015 5:48 pm

Thanks Martin!!! :D

You have been very helpfull!


One last thing..

When I suppose to send "a NULL" to a device and more specific #define SPI_NULL (uint8_t) 0xF0
> What do they mean?
To just send via SPI macro a byte OR character with zero value?

I am suppose to that before I can read data from a specific device.

They gave me this guidelines

#define SPI_NULL (uint8_t) 0xF0
#define SPI_ESC (uint8_t) 0xF1
#define SPI_F0 (uint8_t) 0x00
#define SPI_F1 (uint8_t) 0x01
#define SPI_SYNC (uint8_t) 0x02
#define SPI_XON (uint8_t) 0x03
#define SPI_XOFF (uint8_t) 0x04
#define SPI_ERR (uint8_t) 0x05

When you want to receive the data from WizFi250, You have to send SPI_NULL(0xF0) to WizFi250 using SPI interface like below.

>> CS to Low
>> Microseconds delay (10ms)
>> SPI Send NULL to WizFi250
>> Recive the data at the same clock that was sent SPI_NULL
>> Microseconds delay (10ms)
>> CS to High
:



AND THIS LINK BUT I CANNOT MAKE ANY OUT OF IT, I DO NOT KNOW THE ARDUINO LANGUAGE

https://github.com/Wiznet/Arduino_WizFi250


Thank you,

Best Regards,

Andreas Achilleos

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Re: Watchdoc timer connecting and setting prescaler

Postby Benj » Tue Nov 03, 2015 6:12 pm

Hello Andreas,

For SPI you would typically only ever read or write however both are done simultaneously on every SPI transaction. I would guess that the SPI null value is arbitrary meaning it can literally be anything. So the code would look something like this.

>> CS to Low
>> Microseconds delay (10ms)
>> data = SPI Receive - Read byte from module
>> Microseconds delay (10ms)
>> CS to High

The value sent out for a receive is currently fixed to 0x55 using the SPI Master component. However if you instead use the CAL_SPI component then there is no macros for read or write, only a generic Master_Byte which allows you to read and write simultaneously.

10ms also seems like a big delay, should this be us or even ns? Edit aha I see now you have put Microseconds delay. DOH. :D
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Re: Watchdoc timer connecting and setting prescaler

Postby achillis1 » Tue Nov 03, 2015 7:44 pm

:D

Hello Ben,

Thanks for the reply. Well it is confusing, they say microseconds and they have "ms" which stands for milliseconds yes? :!: I will have to confirm that!


The value sent out for a receive is currently fixed to 0x55 using the SPI Master component. However if you instead use the CAL_SPI component then there is no macros for read or write, only a generic Master_Byte which allows you to read and write simultaneously.


So I guess by saying that , in the SPI macro RECEIVE component there is embedded code that SENDS first 0x55 and then it RECEIVES?

If so, then based on the device instructions I should change that to 0xF0 ?


However if you instead use the CAL_SPI component then there is no macros for read or write, only a generic Master_Byte which allows you to read and write simultaneously.


I have no idea what you mean here! Should I do that? :D (I use FlowcodeV4)

Thank you

Best Regards,

Andreas Achilleos

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Re: Watchdoc timer connecting and setting prescaler

Postby Benj » Wed Nov 04, 2015 11:21 am

Hi Andreas,

Aha sorry I thought you were using v6, in v4 you probably need to use the component customisation to override the outgoing value for receives.

in the SPI macro RECEIVE component there is embedded code that SENDS first 0x55 and then it RECEIVES?


No the send and receive is simultaneous with SPI.

I have never encountered a device that required you to send and receive at the same time so I believe you won't need to customise anything and it should work as is with the new pseudo code breakdown I gave you.
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