pic programming.................. what next?

[tama182]

hey nigel i just noticed, howcome the main board in your tutorial hasn't got anything to clock the pic, theres not crystal or anything

 

[Nigel Goodwin]

hey nigel i just noticed, howcome the main board in your tutorial hasn't got anything to clock the pic, theres not crystal or anything

Try reading the datasheet (or even my tutorials?), one of the reasons for choosing the 628 is that it has an internal 4MHz oscillator - this gives you 16 I/O pins on an 18 pin chip.

 

[bryan1]

Hiya Tama,
Just one question mate since your using the ICD2 have you read the datasheet for for the ICD2?. I ran into similar problems using my ICD2 and a good read of the datasheet explained it all. Oh and just one note NEVER use pullup resistors on the pgc,pgm and use the correct setup for the mlcr pin or you will blow 3 transistors, I'm saying this as I've already been there and done it. But again read the datasheet for the ICD2 and understand it or your new expensive programmer-debuuger could be an expensive paper weight.

Hope this Helps

Cheers Bryan

 

[tama182]

Thanks Bryan, i will read the manual PROPERLY ! before i do anything, unfortunatly im the type that rushes into things and then asks loads of questions before ive even properly read the instructions, LOL :lol:

 

[tama182]

Can anyone see whats wrong with this code, it seems to run fine, until it gets to goto _7SegDisp, where it does goto to the table but then after it has got the binary code, its seems to jump back up to the very first command movlw 0x07

	LIST	p=16F628		;tell assembler what chip we are using
	include "P16F628.inc"		;include the defaults for the chip
	__config 0x3D18			;sets the configuration settings (oscillator type etc.)

	cblock 	0x20 			;start of general purpose registers
		count1 			;used in delay routine
		counta 			;used in delay routine 
		countb 			;used in delay routine
		count
	endc
	
	org	0x0000			;org sets the origin, 0x0000 for the 16F628,
					;this is where the program starts running	
	movlw	0x07
	movwf	CMCON			;turn comparators off (make it like a 16F84)

   	bsf 	STATUS,		RP0	;select bank 1
   	movlw 	b'00000000'		;set PortB all outputs
   	movwf 	TRISB
	bcf		STATUS,		RP0	;select bank 0
	clrf	PORTB



start	clrf	count
read	movfw	count
		goto	_7SegDisp
		movwf	PORTB
		goto	delay
		incf	count,	w
		xorlw	d'14'			;check for last (14th) entry
		btfsc	STATUS,	Z
		goto	start			;if start from beginning
		incf	count,	f		;else do next
		goto	read











_7SegDisp	addwf		PCL		; skips a certain number of instructions
		retlw		b'11111110'	; code for 0
		retlw		b'01100000'	; code for 1
		retlw		b'11011010'	; code for 2
		retlw		b'11110010'	; code for 3
		retlw		b'01100110'	; code for 4
		retlw		b'10110110'	; code for 5
		retlw		b'10111110'	; code for 6
		retlw		b'11100000'	; code for 7
		retlw		b'11111110'	; code for 8
		retlw		b'11110110'	; code for 9
		retlw		b'11101110'	; code for A
		retlw		b'00111110'	; code for b
		retlw		b'10011100'	; code for C
		retlw		b'01111010'	; code for d
		retlw		b'10011110'	; code for E
		retlw		b'10001110'	; code for F


delay	movlw	d'250'			;delay 250 ms (4 MHz clock)
	movwf	count1
d1	movlw	0xC7
	movwf	counta
	movlw	0x01
	movwf	countb
Delay_0
	decfsz	counta, f
	goto	$+2
	decfsz	countb, f
	goto	Delay_0

	decfsz	count1	,f
	goto	d1
	retlw	0x00

	end

 

[Nigel Goodwin]

The program is doing EXACTLY what it's being told to - the reason it doesn't work is because you are using 'goto' instead of 'call' to call subroutines. You do this on both subroutine calls!.

 

[tama182]

oh, so you cant return from a goto instruction, it only remembers its place from a call instruction, is that right,

but if i use a call to go somwhere, and then in that place i use a further goto, to go somwhere else, and then from that place i use the return instruction will i go backl to where i started from, only the next instruction after call?

 

[Nigel Goodwin]

oh, so you cant return from a goto instruction, it only remembers its place from a call instruction, is that right,

but if i use a call to go somwhere, and then in that place i use a further goto, to go somwhere else, and then from that place i use the return instruction will i go backl to where i started from, only the next instruction after call?

When you execute a 'call' the return address is pushed on to the stack, when you you execute a 'return' or 'retlw' the address is popped back off the stack. Goto instructions don't affect this in any way - by executing a 'return' without the previous 'call' there isn't a return address to recover, so the stack will 'under-flow' and return an unknown value.

The PIC stack is also extremely small, so you need to be careful about how many nested subroutines you call, and make sure that you always return from them correctly - this applies to ANY processor, but is particularly important with such a small stack.

 

[tama182]

yes i have read all about stack, when using the pic16f54 i only had two, and i know that its first on, last off, if you have more than two say, so i need to make sure that if i add one on top, i must remove it if i want the next one,

im sorry but i didn't know that you cant retuen from a goto, but now it makes sense why it didn't work,

at the moment i am trying out 7 segs as you may have seen, i thought that it might be a nice tutorial for you to add to your list, such as strobing, which i haven't done yet

 

[Pommie]

oh, so you cant return from a goto instruction, it only remembers its place from a call instruction, is that right,

but if i use a call to go somwhere, and then in that place i use a further goto, to go somwhere else, and then from that place i use the return instruction will i go backl to where i started from, only the next instruction after call?

Yes. But, be aware that PICs can only remember 8 places to return to. This does not mean that you can only use 8 calls but that if you call code after a call but before it returns, it then has to remember 2 return address'.

EG

        call Sub1
        more code

Sub1  call  sub2
         return

Sub2 return

The above code has to remember 2 address'.

As you write more code you will realise that this is quite a big limitation. Your code might call ShowMenu which calls PrintString which calls PrintChar which calls SendBit etc. And, during all this interrupts come along and they have to remember where to return to as well.

Phew

Mike.

 

[Nigel Goodwin]

And, during all this interrupts come along and they have to remember where to return to as well.

Which is an excellent reason NEVER to use subroutines called from interrupt routines! - it just adds more chances to over-flow.

 

[Pommie]

Wow, 2 replies in less time than it took to write mine.

I didn't notice that the OP was using a 16f54 and therefore the stack is even smaller - it can only remember 2 locations to return to.

For learning purposes, it might be better to switch to something like a 16F628A as this will be more capable as you learn more.

Mike.

 

[tama182]

no, im using 16f628 now, its just that the first book i read used 16f54

 

[tama182]

hey nigel, what do you think of this, i messed round with on of you circuits so that it only takes on switch to change the tables

LIST	p=16F628		;tell assembler what chip we are using
	include "P16F628.inc"		;include the defaults for the chip
	__config 0x3D18			;sets the configuration settings (oscillator type etc.)

	cblock 	0x20 			;start of general purpose registers
		count1 			;used in delay routine
		counta 			;used in delay routine 
		countb 			;used in delay routine
		count			;MAIN 14 COUNT
	endc
	
LEDPORT	Equ	PORTB			;set constant LEDPORT = 'PORTB'
LEDTRIS	Equ	TRISB			;set constant for TRIS register
SWPORT	Equ	PORTA
SWTRIS	Equ	TRISA
SW1	Equ	4			;set constants for the switches

LED1	Equ	3			;and for the LED's
LED2	Equ	2
LED3	Equ	1
LED4	Equ	0

	
	org	0x0000			;org sets the origin, 0x0000 for the 16F628,
					;this is where the program starts running	
	movlw	0x07
	movwf	CMCON			;turn comparators off (make it like a 16F84)

   	bsf 	STATUS,		RP0	;select bank 1
   	movlw 	b'00000000'		;set PortB all outputs
   	movwf 	LEDTRIS
	movlw 	b'11110000'		;set PortA 4 inputs, 4 outputs
   	movwf 	SWTRIS
	bcf	STATUS,		RP0	;select bank 0
	clrf	LEDPORT			;set all outputs low
	clrf	SWPORT			;make sure all LED's are off
	BSF		SWPORT, LED1

start1	CLRF	count
		MOVFW	count


Start	movfw	count
		btfsc	SWPORT,	LED1		;check which LED is lit
		call	Table1			;and read the associated table
		btfsc	SWPORT,	LED2
		call	Table2
		btfsc	SWPORT,	LED3
		call	Table3
		btfsc	SWPORT,	LED4
		call	Table4
		movwf	LEDPORT
		incf	count,	w
		xorlw	d'14'			;check for last (14th) entry
		btfsc	STATUS,	Z
		goto	start1			;if start from beginning
		incf	count,	f
		CALL	DELAY
		GOTO	Start


Table1	ADDWF   PCL, f			;data table for bit pattern
	retlw	b'10000000'
        retlw   b'01000000'
        retlw   b'00100000'
        retlw   b'00010000'
        retlw   b'00001000'
        retlw   b'00000100'
        retlw   b'00000010'
        retlw   b'00000001'
        retlw   b'00000010'
        retlw   b'00000100'
        retlw   b'00001000'
        retlw   b'00010000'
        retlw   b'00100000'
        retlw   b'01000000'

Table2	ADDWF   PCL, f			;data table for bit pattern
	retlw	b'11000000'
        retlw   b'01100000'
        retlw   b'00110000'
        retlw   b'00011000'
        retlw   b'00001100'
        retlw   b'00000110'
        retlw   b'00000011'
        retlw   b'00000011'
        retlw   b'00000110'
        retlw   b'00001100'
        retlw   b'00011000'
        retlw   b'00110000'
        retlw   b'01100000'
        retlw   b'11000000'

Table3	ADDWF   PCL, f			;data table for bit pattern
	retlw	b'01111111'
        retlw   b'10111111'
        retlw   b'11011111'
        retlw   b'11101111'
        retlw   b'11110111'
        retlw   b'11111011'
        retlw   b'11111101'
        retlw   b'11111110'
        retlw   b'11111101'
        retlw   b'11111011'
        retlw   b'11110111'
        retlw   b'11101111'
        retlw   b'11011111'
        retlw   b'10111111'

Table4	ADDWF   PCL, f			;data table for bit pattern
	retlw	b'00111111'
        retlw   b'10011111'
        retlw   b'11001111'
        retlw   b'11100111'
        retlw   b'11110011'
        retlw   b'11111001'
        retlw   b'11111100'
        retlw   b'11111100'
        retlw   b'11111001'
        retlw   b'11110011'
        retlw   b'11100111'
        retlw   b'11001111'
        retlw   b'10011111'
        retlw   b'00111111'



Switch1 BTFSC	SWPORT, LED1
		GOTO 	JUMP1
		BTFSC	SWPORT, LED2
		GOTO 	JUMP2
		BTFSC	SWPORT, LED3
		GOTO 	JUMP3
		BTFSC	SWPORT, LED4
		GOTO 	JUMP4
		retlw	0x00

JUMP1	BCF	SWPORT, LED1
		BSF	SWPORT, LED2
		BCF	SWPORT, LED3
		BCF	SWPORT, LED4
		GOTO	BACK

JUMP2	BCF	SWPORT, LED1
		BCF	SWPORT, LED2
		BSF	SWPORT, LED3
		BCF	SWPORT, LED4
		GOTO	BACK

JUMP3	BCF	SWPORT, LED1
		BCF	SWPORT, LED2
		BCF	SWPORT, LED3
		BSF	SWPORT, LED4
		GOTO	BACK

JUMP4	BSF	SWPORT, LED1
		BCF	SWPORT, LED2
		BCF	SWPORT, LED3
		BCF	SWPORT, LED4
		GOTO	BACK



DELAY	movlw	d'250'			;delay 250 ms (4 MHz clock)
	movwf	count1
d1	call 	ChkKeys 		;check the keys
	movlw	0xC7			;delay 1mS
	movwf	counta
	movlw	0x01
	movwf	countb
Delay_0
	decfsz	counta, f
	goto	$+2
	decfsz	countb, f
	goto	Delay_0

	decfsz	count1	,f
	goto	d1
	retlw	0x00

ChkKeys	btfss	SWPORT,	SW1
	call	Switch1
BACK

	retlw	0x00


	end

[/quote]

 

[Nigel Goodwin]

hey nigel, what do you think of this, i messed round with on of you circuits so that it only takes on switch to change the tables

That's what the tutorials are there for, tested working examples that you can alter around to do what you want

 

[tama182]

How come that all the circuits and icd2 manual have a pull up resister for MCLR, i know that its logic 0 activated, but i thought that the pins on IC's go high if there not connected,

so why is a pull up needed?

also you cant use pull ups on PGC/PGD, again doesn't the same apply here,

so does this mean that you basicly cant use R6 and R7 as logic 0 activated switches, because you couldn't have them usually pulled up when not pressed,

but you could have them as logic 1 activated switches, where they would usually be pulled down, when not pressed.

 

[Nigel Goodwin]

How come that all the circuits and icd2 manual have a pull up resister for MCLR, i know that its logic 0 activated, but i thought that the pins on IC's go high if there not connected,

Why did you think that?, it's not true.

With CMOS inputs (like in a PIC) it's important to have the input pins connected to 'something', otherwise their high impedance 'may' allow the pin to drift high, increasing supply current many times, and possibly even triggering the input.

so why is a pull up needed?

To pull the reset pin high.

also you cant use pull ups on PGC/PGD, again doesn't the same apply here,

so does this mean that you basicly cant use R6 and R7 as logic 0 activated switches, because you couldn't have them usually pulled up when not pressed,

but you could have them as logic 1 activated switches, where they would usually be pulled down, when not pressed.

You should pull them high or low, with resistors, to ensure the default state, then switch to the other state. PortB on most PIC's has internal pull-ups, which can be enabled by a bit in a register.

 

[tama182]

You should pull them high or low, with resistors, to ensure the default state, then switch to the other state

Well im just following the ICD2 manual, but when it says that you can't use pull ups on the pgc and pgd inputs, this is just for the programming right?

so if i was to have pull ups on on RB6 and RB7, i could put them on after the programming, is that right?

 

[Nigel Goodwin]

You should pull them high or low, with resistors, to ensure the default state, then switch to the other state

Well im just following the ICD2 manual, but when it says that you can't use pull ups on the pgc and pgd inputs, this is just for the programming right?

so if i was to have pull ups on on RB6 and RB7, i could put them on after the programming, is that right?

Yes, assuming that was what you wanted to do - but designing for ICSP always places constraints on the target design.

 

[tama182]

ok, im just beginning the LCD tutorials now, and im reading through it, and im looking at the table from the pdf of that electronics site that you've got on the first tutorial,

right i understand that your sending the data in nibbles to save pins, but where does the data get saved, because at first i thought that the circuit was strobing, but then i noticed the program only gets run once and then repeats that last last forever,

so you sending the bits in 4, in the table a capital H is 0100 upper and 1000 lower,

so first you send the 0100 to lcd port, pins 0,1,2,3 which on the lcd is data lines 4-7,

but then you send the lower 1000 number, which then over writes 0100, because you used the mov command,

does the 0100 get saved somwhere?

is there memmory or somthing in the lcd, because each nibble you add overwrites the last nibble, so how does each letter get saved, i mean it has to be saved because the program only runs once

(kinda whshing you didn't write the tutorial now ..huh? :roll: )