Please Help

[Elbobbo]

The project I am currently doing asks me the following:
write a program for a PIC16F84A that converts your a number (10 ASCII characters), one character at a time, to the excess-three code. Each converted character is to be displayed on 4 LEDs connected to Port B (B0 to B3) of the microcontroller. Further, each converted character will be ON for 4 second and OFF for 1 second. Once all characters have been displayed the program will continue to run with all the LEDs flashing (ON for 1 second and OFF for 1 second then repeat this infinitely).

So far I don't have much,

Firstly I am unsure how to call a particular digit from the number eg "0" from "0648321975"

I under stand that I'll subtract 48(decimal) from the number (ASCII "0"="48" decimal - 48 decimal), and then add (3) to get the excess three value (3) then Plug this into Port B(B0 to B3) followed by a delay of a second, then turn off/ initialise Port B again.
Using a counter to count the amount of numbers( if under 10 processed got to start again) ( if more than 10 got to the flashing sequence)

Any help will be greatly appreciated.
Cheers

 

[Ian Rogers]

1)First make a table of all the characters:- 0648321975
2)Set the port pin directions
3)Set a variable to count down from 10
4)Create a loop to look at each character in the table in turn
5)Within the loop, load the character and deduct 48 and simply put it on PORTB and delay
6)Create a forever loop to flash the LED's..

 

[Colin]

Are you doing it in assembly?

PIC84 went out with the ark. You must have a very erudite teacher.

 

[Ian Rogers]

Are you doing it in assembly?

PIC84 went out with the ark. You must have a very erudite teacher.

They still use the 6800 here in England... Can't get my head around that one..

 

[Colin]

"They still use the 6800 here in England"

Where is England?

 

[Elbobbo]

Yeah first year elec engineering for a computer engineering subject.
I hardly understand what they are talking about in lectures. I have been reading pic microcontrollers by bates to get a good grip on it.

 

[Elbobbo]

Yes in assembly. I am learning it as I go at the moment. Using MPLAB IDE.

 

[jpanhalt]

How is the ASCII number being presented to the MCU? I did something similar awhile back in which the ASCII characters were entered like this:

Freq                  
                addwf   PCL,f
                dt      "05000000",0

In that case, the ASCII string was included in the code, and I just stepped through the values and tested for zero to end the loop. It was presented here: https://www.electro-tech-online.com/articles/demo-assembly-code-ad9850-dds-signal-generator.755/

Obviously, it doesn't do the 3-excess coding and converts the ASCII to an actual value (slowly), but the initial part (see: user defined frequency in the link) may give you some help. The instruction sets for the 12F683 and 16F84A are the same. Banking may be a bit different.

Edit: Once you extract the individual ASCII, you can go directly to a table with an offset or convert the individual ASCII to hex or dec and go to to a non-offset table to get your Excess-3 code for display on your LED's.

John

 

[Elbobbo]

How is the ASCII number being presented to the MCU? I did something similar awhile back in which the ASCII characters were entered like this:

Freq              
                addwf   PCL,f
                dt      "05000000",0

In that case, the ASCII string was included in the code, and I just stepped through the values with tested for zero to end the loop. It was presented here: https://www.electro-tech-online.com/articles/demo-assembly-code-ad9850-dds-signal-generator.755/

Obviously, it doesn't do the 3-excess coding and converts the ASCII to an actual value (slowly), but the initial part (see: user defined frequency in the link) may give you some help. The instruction sets for the 12F683 and 16F84A are the same. Banking may be a bit different.

John

Yes similar to yours as,

; Student number ASCII table ..............................

snum addwf PCL,F
dt "0061076281" ;Student number

 

[Colin]

You have to start by making a template for PIC16F84 in Notepad

 

[Elbobbo]

This is my flowchart at the moment,

supposed to have YES coming off to the LED flashing and NO to continue down the flowchart

 

[Elbobbo]

this is what i got so far

 

[Colin]

This is all wrong:


; Initialise Port B .................................

BCF status, RP0 ; bit clear
CLRF PORTB ; Initialize PORTB by
; clearing out data latches
BSF status, RP0 ; Select Blank 1
MOVLW 0x10 ; value used to initialise data direction

MOVWF TRISB ; Set RA,<3:0> as outputs
; RA4 as input
; TRISB <7:5> are always read as '0'

 

[Elbobbo]

; Initialise Port B .................................

BCF STATUS, RP0 ;

CLRF PORTB ; Initialize PORTB by clearing output data latches

BSF STATUS, RP0 ; Select Bank 1

MOVLW F0 ; Value used to initialize data direction

MOVWF TRISB ; Set RB<3:0> as outputs
; RB<7:4> as inputs



Any better?

 

[Colin]

When you are in bank0, the operation clrf portB is actually operating on the tris register and making all pins output.

 

[Elbobbo]

So i guess i can just use the operation clrf portB without the rest, since I actually don't need any inputs.

 

[Colin]

You have to make portB output and then you can make all outputs LOW, if you want to.

The first thing you have to do is create a 1 sec delay

 

[Elbobbo]

ok, well i am stuffed. I dont have a clue what I am doing.

I am trying to get the code to look up one of the ASCII characters at a time, using the combination of STRLEN and ASCLEN. But i just cant get my head around it.

 

[Colin]

Does the program deal with a single number or can you import a new number?

 

[Elbobbo]

just the one number, 10 characters long