Question about Nigel Goodwins tutorials - Electronic Circuits Projects Diagrams Free

sbdwag · 6th March 2007, 04:18 PM

One question about the sample code provided by Nigel Goodwin

at the bottom part of the delay loops the command "goto $+2" ? Where is it going to ?

Regards
Dennis

Delay_0
decfsz counta, f
goto $+2
decfsz countb, f
goto Delay_0

decfsz count1 ,f
goto d1
retlw 0x00

++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++

;Tutorial 1.2 - Nigel Goodwin 2002
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
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
movwf TRISA ;set PortA all outputs
bcf STATUS, RP0 ;select bank 0

Loop
movlw 0xff
movwf PORTA ;set all bits on
movwf PORTB
nop ;the nop's make up the time taken by the goto
nop ;giving a square wave output
call Delay ;this waits for a while!
movlw 0x00
movwf PORTA
movwf PORTB ;set all bits off
call Delay
goto Loop ;go back and do it again

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

williB · 6th March 2007, 04:31 PM

that means jump two lines forward.

sbdwag · 6th March 2007, 04:41 PM

Thanks Ive looked all over for that even spent 60 dollars for a book looking for that. Thought it was refering to a hex location plus two

Got any good sources for answers to questions like this one.

Thanks again

Dennis

**Nigel Goodwin** · 6th March 2007, 05:02 PM

Quote:

Originally Posted by sbdwag

Thanks Ive looked all over for that even spent 60 dollars for a book looking for that. Thought it was refering to a hex location plus two

Got any good sources for answers to questions like this one.

Where it came from, the MPASM helpfile - $ simply refers to the current address - $+1 is a common use, essentially a NOP, but it takes twice as long as a NOP, so it makes a double length NOP.

blueroomelectronics · 6th March 2007, 05:34 PM

Code:

goto $+2

Got to be careful with that if you plan on using 18 series chips.

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6th March 2007, 04:18 PM	(permalink)
sbdwag	Question about Nigel Goodwins tutorials One question about the sample code provided by Nigel Goodwin at the bottom part of the delay loops the command "goto $+2" ? Where is it going to ? Regards Dennis Delay_0 decfsz counta, f goto $+2 decfsz countb, f goto Delay_0 decfsz count1 ,f goto d1 retlw 0x00 ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++ ;Tutorial 1.2 - Nigel Goodwin 2002 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 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 movwf TRISA ;set PortA all outputs bcf STATUS, RP0 ;select bank 0 Loop movlw 0xff movwf PORTA ;set all bits on movwf PORTB nop ;the nop's make up the time taken by the goto nop ;giving a square wave output call Delay ;this waits for a while! movlw 0x00 movwf PORTA movwf PORTB ;set all bits off call Delay goto Loop ;go back and do it again 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

6th March 2007, 04:31 PM	(permalink)
williB	that means jump two lines forward.

6th March 2007, 04:41 PM	(permalink)
sbdwag	Thanks Ive looked all over for that even spent 60 dollars for a book looking for that. Thought it was refering to a hex location plus two Got any good sources for answers to questions like this one. Thanks again Dennis

6th March 2007, 05:34 PM	(permalink)
blueroomelectronics	Code: goto $+2 Got to be careful with that if you plan on using 18 series chips. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com