First steps with PIC16F819

[Robbs]

I've written/plagiarized the following, as my first attempt to do anything
with a microcontroller:

------------------------------------------------------begin code------


list p=16f819 ; list directive to define processor
#include <p16F819.inc> ; processor specific variable definitions

errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _CCP1_RB2 & _DEBUG_OFF &
_LVP_OFF & _BODEN_OFF & _MCLR_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_IO


main

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches
BANKSEL ADCON1 ; Select Bank of ADCON1
MOVLW 0x06 ; Configure all pins
MOVWF ADCON1 ; as digital inputs
MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Set RA<7:0> as outputs
MOVLW 0xAA ; Output '10101010b' to
; PORTA (I hope)


; initialize eeprom locations

ORG 0x2100
DE 0x00, 0x01, 0x02, 0x03


END ; directive 'end of program'

-----------------------------------------------------------end
code-------------


Will this do what I hope it will, simply output 10101010b (0xAA) to PORTA?
If so, is it safe to check the pins with a voltmeter between the I/O pin and
Vss? would a series resistor be wise?

Thank you very much,

Robbs

 

[Robbs]

Funny how seeing your post in an actual ng can make you see errors. Sorry,
with corrections:
------------------------------------------------------------

list p=16f819 ; list directive to define processor
#include <p16F819.inc> ; processor specific variable definitions

errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _CCP1_RB2 & _DEBUG_OFF &
_LVP_OFF & _BODEN_OFF & _MCLR_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_IO


main

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches
BANKSEL ADCON1 ; Select Bank of ADCON1
MOVLW 0x06 ; Configure all pins
MOVWF ADCON1 ; as digital inputs
MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Set RA<7:0> as outputs
MOVLW 0xAA ; Output '10101010b' to
; PORTA (in theory)


; initialize eeprom locations

ORG 0x2100
DE 0x00, 0x01, 0x02, 0x03


END ; directive 'end of program'

 

[Robbs]

Sorry. With corrections:



list p=16f819 ; list directive to define processor
#include <p16F819.inc> ; processor specific variable definitions

errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _CCP1_RB2 & _DEBUG_OFF &
_LVP_OFF & _BODEN_OFF & _MCLR_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_IO


main

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches

BANKSEL TRISA ; Select Bank of TRISA
MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Actually write the
; value to the register

BANKSEL PORTA ; select bank of PORTA
MOVLW 0xAA ; Output '10101010b' to
; PORTA (in theory)
MOVWF PORTA ; Set RA<7:0> as outputs



; initialize eeprom locations

ORG 0x2100
DE 0x00, 0x01, 0x02, 0x03


END ; directive 'end of program'


------------------------------------------end code-----------
Will this do what I hope it will, simply output 10101010b (0xAA) to PORTA?
If so, is it safe to check the pins with a voltmeter between the I/O pin and
Vss? would a series resistor be wise?

Is the last bit of code necessary, under 'initialize eeprom locations'? it
was part of the example code supplied with MPLABS, and I'm not sure exactly
what it does.

I realize that one pin on PORTA (pin 5, i think) is an input only.

Thank you very much,

Robbs

 

[Ishaan Dalal]

Sorry. With corrections:

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches

BANKSEL TRISA ; Select Bank of TRISA

MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Actually write the
; value to the register

CLRF TRISA will do just as well.

BANKSEL PORTA ; select bank of PORTA
MOVLW 0xAA ; Output '10101010b' to
; PORTA (in theory)
MOVWF PORTA ; Set RA<7:0> as outputs

Code looks OK, comments are skewed -- MOVLW 0xAA moves the literal to the W
reg, while MOVWF PORTA actually outputs 0xAA to PORTA.

Will this do what I hope it will, simply output 10101010b (0xAA) to PORTA?
Yes.

If so, is it safe to check the pins with a voltmeter between the I/O pin and
Vss? would a series resistor be wise?

Yes; no series resistor needed; but 8 LEDs with series resistors might be
easier to decode.

Is the last bit of code necessary, under 'initialize eeprom locations'? it
was part of the example code supplied with MPLABS, and I'm not sure exactly
what it does.

Not for whatever your main code does.

I realize that one pin on PORTA (pin 5, i think) is an input only.

Then that pin is permanently tri-stated -- you will see nothing on that pin,
unless you force it by using a pull-up or pull-down resistor.

 

[Leon Heller]

I've written/plagiarized the following, as my first attempt to do anything
with a microcontroller:

------------------------------------------------------begin code------


list p=16f819 ; list directive to define processor
#include <p16F819.inc> ; processor specific variable definitions

errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _CCP1_RB2 & _DEBUG_OFF &
_LVP_OFF & _BODEN_OFF & _MCLR_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_IO


main

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches
BANKSEL ADCON1 ; Select Bank of ADCON1
MOVLW 0x06 ; Configure all pins
MOVWF ADCON1 ; as digital inputs
MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Set RA<7:0> as outputs
MOVLW 0xAA ; Output '10101010b' to
; PORTA (I hope)


; initialize eeprom locations

ORG 0x2100
DE 0x00, 0x01, 0x02, 0x03


END ; directive 'end of program'

-----------------------------------------------------------end
code-------------


Will this do what I hope it will, simply output 10101010b (0xAA) to PORTA?
If so, is it safe to check the pins with a voltmeter between the I/O pin and
Vss? would a series resistor be wise?

It would be a good idea to end main with something like

stop:
goto stop

checking with a meter is OK, you don't need a resistor.

Leon

 

[Michel Catudal]

Sorry. With corrections:



list p=16f819 ; list directive to define processor
#include <p16F819.inc> ; processor specific variable definitions

errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _CCP1_RB2 & _DEBUG_OFF
&
_LVP_OFF & _BODEN_OFF & _MCLR_OFF & _WDT_OFF & _PWRTE_ON & _INTRC_IO


main

BANKSEL PORTA ; select bank of PORTA
CLRF PORTA ; Initialize PORTA by
; clearing ouput
; data latches

BANKSEL TRISA ; Select Bank of TRISA
MOVLW 0x00 ; Value used to
; inititalize data
; direction
MOVWF TRISA ; Actually write the
; value to the register

BANKSEL PORTA ; select bank of PORTA
MOVLW 0xAA ; Output '10101010b' to
; PORTA (in theory)
MOVWF PORTA ; Set RA<7:0> as outputs



; initialize eeprom locations

ORG 0x2100
DE 0x00, 0x01, 0x02, 0x03


END ; directive 'end of program'


------------------------------------------end code-----------
Will this do what I hope it will, simply output 10101010b (0xAA) to PORTA?
If so, is it safe to check the pins with a voltmeter between the I/O pin
and Vss? would a series resistor be wise?

Is the last bit of code necessary, under 'initialize eeprom locations'? it
was part of the example code supplied with MPLABS, and I'm not sure
exactly what it does.

I realize that one pin on PORTA (pin 5, i think) is an input only.

Thank you very much,

Robbs

Your program will do unexpected things after it crashes at the end of your code.
This is not a PC, you must provide some code to either rerun some of the same
code, some other code or do nothing. The way you wrote it, it will run whatever
garbage follows your code.