I/O Pin status during startup

[PaulMaker]

Hi guys,

quick question...

Is there a way (somewhere on the datasheet for example) to know what are the I/O pins state during power up?
I've noticed that some I/O pins (on my 18F2580 MCU) start high even placing "clear" and "PORTA=000000, PORTB=000000, PORTC=000000) at the start of the code (when i say start, i mean after all the configuration lines).
I currently have the "INCLUDE "ALLDIGITAL.pbp"" before the actual code start.

How can I force all the I/Os to be low until the code tells them to go high?

Thanks

[Acetronics2]

no defined I/Os state before you set it ...

the one and only way is an external pull up or down resistor, as I/Os are placed in an INPUT state ( High impedance ) @ power up ...

moreover, you have to manually set input state before some PBP Commands ( pulsin, RC Time, Toggle ... ) to be sure of what you get.

Alain

[PaulMaker]

Hi Acetronics2,
thanks for your reply.

To be accurate, during power on, these I/Os turn on and off (and then stay off) very quickly (like a flash). The idea is to stop that high-low behavior.

[Jerson]

Hi
To be accurate, during power on, these I/Os turn on and off (and then stay off) very quickly (like a flash). The idea is to stop that high-low behavior.

Simple answer- you cannot do that.

You should design your project with active low outputs to account for the High-Z input state at power on. Almost every microcontroller, I know, behaves similarly unless there is special hardware built in to retain a certain state at power on. Till such time as your program code runs, the microcontroller IO pins are kept in a High-Z state to prevent unintentional damage to itself.

[PaulMaker]

Greetings,

thank you Jerson for your reply.

Regarding "design your project with active low outputs to account for the High-Z input state at power on", what do you mean exactly?
If, for example, I only have LEDs on these I/Os, what can I do?

[richard]

if you have leds that illuminate on power up before the pins have been set as outputs then you are doing something very odd
or you have broken something

schematic and code ?

[HenrikOlsson]

Yeah, this sounds very strange.

As others have said, after power on and reset (POR) all the pins come up as inputs so they should not go either high or low for any duration. Leakage current into the pin is MUCH less than a uA (200nA max) so basically "any" sort of resistance (ie several mega Ohms) to either Vdd or Vss will pull the pin to that.

And it doesn't really matter what you do with the PORT or LAT registers until you also clears the TRIS bits in questions. Ie, at power up the pins are inputs (high impedence), then you "preset" their default state(s) by writing to PORT or LAT and finally you clear the corresponding TRIS bits to enable the output drivers.

The 18F2580 have pull-ups on PORTB (and PORTB only it seems). They are disabled on POR so they should not be able to pull the pin high. The current sourced thru the pull-up resistor is between 50 and 400uA so even WITH them enabled I don't think you'd see a LED light up.

More details please...

[Jerson]

Greetings,

thank you Jerson for your reply.

Regarding "design your project with active low outputs to account for the High-Z input state at power on", what do you mean exactly?
If, for example, I only have LEDs on these I/Os, what can I do?

Many a times, I have used an I/O pin to drive a relay through a transistor. So, assuming I need an active high output to turn on the relay, I have observed (across microcontroller families) that the relay flicks on for the fraction of a second till the program code takes control and the pin get set to the off - state of the relay (0). So, the ideal way to resolve such a situation is to ensure that the relay turns on only when the I/O pin is made to output a LOW.

In case of driving an LED from an IO pin, my thinking is biased with the TTL logic output specificiation where the sinking current limit is larger than the sourcing current limit. So, I usually tend to use LEDS with an active low output configuration. The IO port has to be low for the LED to turn on. This spec thing is no longer true with the current generation of microcontrollers except the 8051 family dies from old.

So, as a best practice, I tend to use active low outputs for any device that needs to be turned on.

[Acetronics2]

I Never saw something like that ....

but, if we consider LEDs as current generators when illuminated ( Yes, the built in input clamp diodes ... )

the question comes ... is the pic in a true OFF state @ "powerup" ???

THE ONE and ONLY thing to have here is ...

SHOW US the full Pic program ( with config ! ) and the Circuit real scheme.

already asked for @ #6 !!!

Alain

[PaulMaker]

Greetings all,

thank you all for your inputs.

Here is the code:

'****************************************************************'*  Name    : Led Controller.PBP                                *
'*  Author  : Paul Maker                                        *
'*  Notice  : Copyright (c) 2024 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 19/12/2024                                        *
'*  Version : 1.0                                               *
'*  Notes   : 18F2580                                           *
'*          :                                                   *
'****************************************************************
'
'
'
;----[18F2580 Hardware Configuration]-------------------------------------------
#IF __PROCESSOR__ = "18F2580"
  #DEFINE MCU_FOUND 1
#CONFIG
  CONFIG  OSC = IRCIO67      ; Internal oscillator block, port function on RA6 and RA7
  CONFIG  FCMEN = OFF        ; Fail-Safe Clock Monitor disabled
  CONFIG  IESO = OFF         ; Oscillator Switchover mode disabled
  CONFIG  PWRT = OFF         ; PWRT disabled
  CONFIG  BOREN = OFF        ; Brown-out Reset disabled in hardware and software
  CONFIG  BORV = 3           ; VBOR set to 2.1V
  CONFIG  WDT = OFF          ; WDT disabled (control is placed on the SWDTEN bit)
  CONFIG  WDTPS = 512        ; 1:512
  CONFIG  PBADEN = OFF       ; PORTB<4:0> pins are configured as digital I/O on Reset
  CONFIG  LPT1OSC = OFF      ; Timer1 configured for higher power operation
  CONFIG  MCLRE = OFF        ; RE3 input pin enabled; MCLR disabled
  CONFIG  STVREN = ON        ; Stack full/underflow will cause Reset
  CONFIG  LVP = OFF          ; Single-Supply ICSP disabled
  CONFIG  BBSIZ = 1024       ; 1K words (2K bytes) boot block
  CONFIG  XINST = OFF        ; Instruction set extension and Indexed Addressing mode disabled (Legacy mode)
  CONFIG  DEBUG = OFF        ; Background debugger disabled, RB6 and RB7 configured as general purpose I/O pins
  CONFIG  CP0 = OFF          ; Block 0 (000800-001FFFh) not code-protected
  CONFIG  CP1 = OFF          ; Block 1 (002000-003FFFh) not code-protected
  CONFIG  CP2 = OFF          ; Block 2 (004000-005FFFh) not code-protected
  CONFIG  CP3 = OFF          ; Block 3 (006000-007FFFh) not code-protected
  CONFIG  CPB = OFF          ; Boot block (000000-0007FFh) not code-protected
  CONFIG  CPD = OFF          ; Data EEPROM not code-protected
  CONFIG  WRT0 = OFF         ; Block 0 (000800-001FFFh) not write-protected
  CONFIG  WRT1 = OFF         ; Block 1 (002000-003FFFh) not write-protected
  CONFIG  WRT2 = OFF         ; Block 2 (004000-005FFFh) not write-protected
  CONFIG  WRT3 = OFF         ; Block 3 (006000-007FFFh) not write-protected
  CONFIG  WRTC = OFF         ; Configuration registers (300000-3000FFh) not write-protected
  CONFIG  WRTB = OFF         ; Boot block (000000-0007FFh) not write-protected
  CONFIG  WRTD = OFF         ; Data EEPROM not write-protected
  CONFIG  EBTR0 = OFF        ; Block 0 (000800-001FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR1 = OFF        ; Block 1 (002000-003FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR2 = OFF        ; Block 2 (004000-005FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR3 = OFF        ; Block 3 (006000-007FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTRB = OFF        ; Boot block (000000-0007FFh) not protected from table reads executed in other blocks
#ENDCONFIG


#ENDIF


;----[Verify Configs have been specified for Selected Processor]----------------
;       Note: Only include this routine once, after all #CONFIG blocks
#IFNDEF MCU_FOUND
  #ERROR "No CONFIGs found for [" + __PROCESSOR__ +"]"
#ENDIF


'*****************************************************************************


OSCCON =%01110000
OSCTUNE=%11000000


DEFINE OSC 8


'*****************************************************************************


INCLUDE "ALLDIGITAL.pbp"
DEFINE SHOWDIGITAL 1


'*****************************************************************************


INCLUDE "modedefs.bas" 
'DEFINE DEBUGIN_REG PORTB  
'DEFINE DEBUGIN_BIT 5
'DEFINE DEBUGIN_BAUD 1200
'DEFINE DEBUGIN_MODE 0


'*****************************************************************************


TRISA = %00000000				
TRISB = %00100000
TRISC = %00000000


'*****************************************************************************


'PORTS & PINS 


LED1			var		PORTC.1 'IC5
LED2 			var		PORTC.2 'IC5
LED3			var		PORTC.0 'IC5
LED4			var		PORTA.6 'IC5	


LED5			var		PORTB.4 'IC5
LED6			var		PORTA.7 'IC5


LED7 			var 	PORTB.0 'IC5
LED8 			var		PORTB.1 'IC5
LED9 			var		PORTB.2 'IC5
LED10 			var		PORTB.3 'IC5


LED11			var		PORTC.3 'IC5
LED12			var		PORTC.4 'IC5
LED13			var		PORTC.5 'IC5
LED14			var		PORTC.6 'IC5
LED15			var		PORTC.7 'IC5


LED16			var		PORTA.5 'IC5
LED17			var		PORTA.4 'IC5
LED18			var		PORTA.3 'IC5
LED19			var		PORTA.2 'IC5
LED20			var		PORTA.1 'IC5
LED21			var		PORTA.0 'IC5
LED22			var		PORTB.7 'IC5
LED23			var		PORTB.6 'IC5


IC_RX			var		PORTB.5	'IC5 INPUT




CT					VAR		BYTE
CT					VAR		BYTE
PA1   				VAR 	WORD
PA2   				VAR 	WORD
PA3   				VAR 	WORD
PA4   				VAR 	WORD


'*****************************************************************************
INIT:


clear


pause 100


PORTA=%00000000
PORTB=%00000000
PORTC=%00000000


TRISB.5=1


PA1=300
PA2=600
PA3=900
PA4=1500


CT=0
CT2=0


pause 1000


'-----------------------------------------------------------------
START:


pause 400


high LED3
high LED4


pause 1600 


high LED10
high LED15


pause PA4 


high LED1	
high LED2	
high LED6
HIGH LED16


PAUSE 600  


PAUSE PA4	


GOTO ANIM


'-----------------------------------------------------------------
ANIM:


high LED9
high LED14


PAUSE PA3 


high LED8
high LED13


PAUSE PA3 


LOW LED13


PAUSE PA3 


HIGH LED7


PAUSE PA3 


LOW LED7
HIGH LED13


PAUSE PA3 
PAUSE PA3 
PAUSE PA3 


LOW LED8


PAUSE PA3


LOW LED13


PAUSE PA3 
PAUSE PA3 
PAUSE PA3 


HIGH LED8
HIGH LED13


Goto ANIM

Regarding the schematic, I don't have one at the moment but basically it's just the MCU connected to 5V (with 1uF capacitor between VDD and GND pins) and several LEDs connected to each pin (one LED on each pin) in series with a resistor.

[richard]

are the leds connected to gnd or vdd ?
are the leds powered by the same supply?
what size is the led series resistor ?


and what does actually happen compared what you expect to happen

note a schematic can be a picture of a simple hand drawn pencil/paper sketch , or a doodle from paint brush
it does not need to be fancy just readable and complete

[HenrikOlsson]

So, looking at your code....effectively it boils down to

TRISA = %00000000	    ' This enables 23 of 24 output drivers, pins goes to whatever state PORT/LAT says			
TRISB = %00100000
TRISC = %00000000

clear

pause 100                 ' Twiddle thumbs for 100ms

PORTA=%00000000     ' And THEN the pins are set to 0
PORTB=%00000000
PORTC=%00000000

[/code]

You need to do it the other way around.

[PaulMaker]

Hi Richard, thanks for the help.

Regarding the drawing...will try to get it and post here.
In the meantime here are the answers:

are the leds connected to gnd or vdd ?

The LEDs are connected to ground

are the leds powered by the same supply?

Yes, same power supply as the MCU

what size is the led series resistor ?

It's 500ohms for a SMD LED

and what does actually happen compared what you expect to happen

The same moment that i turn the power on, the LEDs turn on and then off very fast.
After some seconds (when the code kicks in) the LED animation starts.

I expect the LEDs not flash when turning the power on and only turn on when the code kicks in.

[richard]

before you go to too much trouble try what henrik suggests

clear all output ports before setting the tris registers and lose that delay in between

[Acetronics2]

did you simply try to add :

INIT:


PORTA=%00000000
PORTB=%00000000
PORTC=%00000000




clear


pause 100




TRISB.5=1




PA1=300
PA2=600
PA3=900
PA4=1500

in the config section ...

[tumbleweed]

did you simply try to add ...

The important part is to set the PORT (or LAT) registers BEFORE setting the TRIS registers to outputs.
Otherwise the pins will be in output mode for a period of time but the outputs aren't specified.

[Acetronics2]

Hi, Tumbleweed

the funny thing is I had added the port setting lines right before the TRIS statements for a run With MPLAB 8.92 sim ...

'****************************************************************'*  Name    : Led Controller.PBP                                *
'*  Author  : Paul Maker                                        *
'*  Notice  : Copyright (c) 2024 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 19/12/2024                                        *
'*  Version : 1.0                                               *
'*  Notes   : 18F2580                                           *
'*          :                                                   *
'****************************************************************
'
'
'
;----[18F2580 Hardware Configuration]-------------------------------------------
#IF __PROCESSOR__ = "18F2580"
  #DEFINE MCU_FOUND 1
#CONFIG
  CONFIG  OSC = IRCIO67      ; Internal oscillator block, port function on RA6 and RA7
  CONFIG  FCMEN = OFF        ; Fail-Safe Clock Monitor disabled
  CONFIG  IESO = OFF         ; Oscillator Switchover mode disabled
  CONFIG  PWRT = OFF         ; PWRT disabled
  CONFIG  BOREN = OFF        ; Brown-out Reset disabled in hardware and software
  CONFIG  BORV = 3           ; VBOR set to 2.1V
  CONFIG  WDT = ON           ; WDT disabled (control is placed on the SWDTEN bit)
  CONFIG  WDTPS = 512        ; 1:512
  CONFIG  PBADEN = OFF       ; PORTB<4:0> pins are configured as digital I/O on Reset
  CONFIG  LPT1OSC = OFF      ; Timer1 configured for higher power operation
  CONFIG  MCLRE = OFF        ; RE3 input pin enabled; MCLR disabled
  CONFIG  STVREN = ON        ; Stack full/underflow will cause Reset
  CONFIG  LVP = OFF          ; Single-Supply ICSP disabled
  CONFIG  BBSIZ = 1024       ; 1K words (2K bytes) boot block
  CONFIG  XINST = OFF        ; Instruction set extension and Indexed Addressing mode disabled (Legacy mode)
  CONFIG  DEBUG = OFF        ; Background debugger disabled, RB6 and RB7 configured as general purpose I/O pins
  CONFIG  CP0 = OFF          ; Block 0 (000800-001FFFh) not code-protected
  CONFIG  CP1 = OFF          ; Block 1 (002000-003FFFh) not code-protected
  CONFIG  CP2 = OFF          ; Block 2 (004000-005FFFh) not code-protected
  CONFIG  CP3 = OFF          ; Block 3 (006000-007FFFh) not code-protected
  CONFIG  CPB = OFF          ; Boot block (000000-0007FFh) not code-protected
  CONFIG  CPD = OFF          ; Data EEPROM not code-protected
  CONFIG  WRT0 = OFF         ; Block 0 (000800-001FFFh) not write-protected
  CONFIG  WRT1 = OFF         ; Block 1 (002000-003FFFh) not write-protected
  CONFIG  WRT2 = OFF         ; Block 2 (004000-005FFFh) not write-protected
  CONFIG  WRT3 = OFF         ; Block 3 (006000-007FFFh) not write-protected
  CONFIG  WRTC = OFF         ; Configuration registers (300000-3000FFh) not write-protected
  CONFIG  WRTB = OFF         ; Boot block (000000-0007FFh) not write-protected
  CONFIG  WRTD = OFF         ; Data EEPROM not write-protected
  CONFIG  EBTR0 = OFF        ; Block 0 (000800-001FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR1 = OFF        ; Block 1 (002000-003FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR2 = OFF        ; Block 2 (004000-005FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTR3 = OFF        ; Block 3 (006000-007FFFh) not protected from table reads executed in other blocks
  CONFIG  EBTRB = OFF        ; Boot block (000000-0007FFh) not protected from table reads executed in other blocks
#ENDCONFIG




#ENDIF




;----[Verify Configs have been specified for Selected Processor]----------------
;       Note: Only include this routine once, after all #CONFIG blocks
#IFNDEF MCU_FOUND
  #ERROR "No CONFIGs found for [" + __PROCESSOR__ +"]"
#ENDIF




'*****************************************************************************




OSCCON =110000
OSCTUNE=000000




DEFINE OSC 8




'*****************************************************************************




INCLUDE "ALLDIGITAL.pbp"
DEFINE SHOWDIGITAL 1




'*****************************************************************************




INCLUDE "modedefs.bas" 
'DEFINE DEBUGIN_REG PORTB  
'DEFINE DEBUGIN_BIT 5
'DEFINE DEBUGIN_BAUD 1200
'DEFINE DEBUGIN_MODE 0




'*****************************************************************************


PORTA = 0
PORTB = 0
PORTC = 0
TRISA = 000000                
TRISB = 100000
TRISC = 000000






'*****************************************************************************




'PORTS & PINS 




LED1            var        PORTC.1 'IC5
LED2             var        PORTC.2 'IC5
LED3            var        PORTC.0 'IC5
LED4            var        PORTA.6 'IC5    




LED5            var        PORTB.4 'IC5
LED6            var        PORTA.7 'IC5




LED7             var     PORTB.0 'IC5
LED8             var        PORTB.1 'IC5
LED9             var        PORTB.2 'IC5
LED10             var        PORTB.3 'IC5




LED11            var        PORTC.3 'IC5
LED12            var        PORTC.4 'IC5
LED13            var        PORTC.5 'IC5
LED14            var        PORTC.6 'IC5
LED15            var        PORTC.7 'IC5




LED16            var        PORTA.5 'IC5
LED17            var        PORTA.4 'IC5
LED18            var        PORTA.3 'IC5
LED19            var        PORTA.2 'IC5
LED20            var        PORTA.1 'IC5
LED21            var        PORTA.0 'IC5
LED22            var        PORTB.7 'IC5
LED23            var        PORTB.6 'IC5




IC_RX            var        PORTB.5    'IC5 INPUT








CT                    VAR        BYTE
CT2                    VAR        BYTE
PA1                   VAR     WORD
PA2                   VAR     WORD
PA3                   VAR     WORD
PA4                   VAR     WORD


clear


'*****************************************************************************
INIT: ' setting the Variables ... )




PA1=300
PA2=600
PA3=900
PA4=1500


pause 1000




'-----------------------------------------------------------------
START:




high LED3
high LED4




pause 1600 




high LED10
high LED15




pause PA4 




high LED1    
high LED2    
high LED6
HIGH LED16




PAUSE 600  




PAUSE PA4    




'-----------------------------------------------------------------
WHILE 1




high LED9
high LED14




PAUSE PA3 




high LED8
high LED13




PAUSE PA3 




LOW LED13




PAUSE PA3 




HIGH LED7




PAUSE PA3 




LOW LED7
HIGH LED13




PAUSE PA3 
PAUSE PA3 
PAUSE PA3 




LOW LED8




PAUSE PA3




LOW LED13




PAUSE PA3 
PAUSE PA3 
PAUSE PA3 




HIGH LED8
HIGH LED13




WEND

With some "cleaning" ( wiped double definitions and "enlighted" the never-ending loop )

MPLAB 8.92 ( the last one ! ) is rather useful for those simple programs debugging using checking breakpoints as it is still working fine with W11 ...

[PaulMaker]

Greetings all,

first of all, thank you so much for all your help.

I tried moving the port settings before the Tris statement like you recommended and it worked!

PORTA=%00000000PORTB=%00000000
PORTC=%00000000


TRISA = %00000000				
TRISB = %00100000
TRISC = %00000000

With this change, the LEDs don't flash anymore during startup.
You guys nailed it!

Thanks

[Acetronics2]

Great !

just remember the processor does what you tell it ... and ONLY what you tell it ! ( thanks to God, PBP doesn't show too many bugs )

so, it's always you to set ALL the parameters, registers, variables ... etc, etc ... and overall take the greatest care of the default settings !

READ THAT F... MANUAL ( )as we were used to write here. ) as a punishment, read carefully manual $ 8.1 ...

Alain