ON VALUE - Revision history

Admin: Created page with "= Action = Branch to one of several specified labels, depending on the value of a variable.
2013-02-11T20:52:05Z

Created page with "= <span class="f_Header">Action</span> = Branch to one of several specified labels, depending on the value of a variable. <span style="font-family: Arial;"> </span> <s..."

New page
= <span class="f_Header">Action</span> =

Branch to one of several specified labels, depending on the value of a variable.

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

= <span class="f_Header">Syntax</span> =

<span class="f_Syntax">ON</span> var [GOTO] [GOSUB] label1 [, label2 ] [,CHECK]

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

= <span class="f_Header">Remarks</span> =
<div style="padding: 0px; margin: 0px 0px 0px 4px;">
{| width="515" cellspacing="0" cellpadding="1" border="1" style="border: 2px solid rgb(0, 0, 0); border-spacing: 0px; border-collapse: collapse;"
|- style="vertical-align: top;"
| valign="top" width="21%" style="width: 105px; border: 1px solid rgb(0, 0, 0);" |
Var

| valign="top" width="98%" style="width: 401px; border: 1px solid rgb(0, 0, 0);" |
The numeric variable to test.

This can also be a SFR such as PORTB.

|- style="vertical-align: top;"
| valign="top" width="21%" style="width: 105px; border: 1px solid rgb(0, 0, 0);" |
label1, label2

| valign="top" width="98%" style="width: 401px; border: 1px solid rgb(0, 0, 0);" |
The labels to jump to depending on the value of var.

|- style="vertical-align: top;"
| valign="top" width="21%" style="width: 105px; border: 1px solid rgb(0, 0, 0);" |
CHECK

| valign="top" width="98%" style="width: 401px; border: 1px solid rgb(0, 0, 0);" |
An optional check for the number of provided labels.

|}
</div>
<span style="font-family: Arial;"> </span>

Note that the value is zero based. So when var is 0, the first specified label is jumped/branched.

It is important that each possible value has an associated label.

When there are not enough labels, the stack will get corrupted. For example :

ON value label1, label2

<span style="font-family: Arial;"> </span>

And value = 2, there is no associated label.

<span style="font-family: Arial;"> </span>

You can use the optional CHECK so the compiler will check the value against the number of provided labels. When there are not enough labels for the value, there will be no GOTO or GOSUB and the next line will be executed.

<span style="font-family: Arial;"> </span>

= <span class="f_Header">See Also</span> =

[[ON INTERRUPT|ON INTERRUPT]]

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

= <span class="f_Header">ASM</span> =

The following code will be generated for a non-MEGA micro with ON value GOTO.

Ldi R26,$60       ; load address of variable

Ldi R27,$00 ; load constant in register

Ld R24,X

Clr R25

<span style="font-family: Arial;"> </span>

Ldi R30, Low(ON_1_ * 1)     ; load Z with address of the label

Ldi R31, High(ON_1_ * 1)

<span style="font-family: Arial;"> </span>

Add zl,r24       ; add value to Z

Adc zh,r25

<span style="font-family: Arial;"> </span>

Ijmp        ; jump to address stored in Z

<span style="font-family: Arial;"> </span>

ON_1_:

<span style="font-family: Arial;"> </span>

Rjmp lbl1       ; jump table

Rjmp lbl2

Rjmp lbl3

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

The following code will be generated for a non-MEGA micro with ON value GOSUB.

<span style="font-family: Arial;"> </span>

<nowiki>;#####</nowiki> On X Gosub L1 , L2

Ldi R30,Low(ON_1_EXIT * 1)

Ldi R31,High(ON_1_EXIT * 1)

Push R30 ;push return address

Push R31

Ldi R30,Low(ON_1_ * 1)      ;load table address

Ldi R31,High(ON_1_ * 1)

Ldi R26,$60

Ld R24,X

Clr R25

<span style="font-family: Arial;"> </span>

Add zl,r24 ; add to address of jump table

Adc zh,r25

Ijmp        ; jump !!!

<span style="font-family: Arial;"> </span>

ON_1_:

Rjmp L1

Rjmp L2

ON_1_EXIT:

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

As you can see a jump is used to call the routine. Therefore the return address is first saved on the stack.

<span style="font-family: Arial;"> </span>

<span style="font-family: Arial;"> </span>

= <span class="f_Header">Example</span> =

<br/><source lang="bascomavr">
'-----------------------------------------------------------------------------------------
'name : ongosub.bas
'copyright : (c) 1995-2005, MCS Electronics
'purpose : demo : ON .. GOSUB/GOTO
'micro : Mega48
'suited for demo : yes
'commercial addon needed : no
'-----------------------------------------------------------------------------------------

$regfile = "m48def.dat" ' specify the used micro
$crystal = 4000000 ' used crystal frequency
$baud = 19200 ' use baud rate
$hwstack = 32 ' default use 32 for the hardware stack
$swstack = 10 ' default use 10 for the SW stack
$framesize = 40 ' default use 40 for the frame space

Dim A As Byte
Input "Enter value 0-2 " , A 'ask for input
Rem Note That The Starting Value Begins With 0
On A Gosub L0 , L1 , L2
Print "Returned"

If Portb < 2 Then 'you can also use the portvalue
On Portb Goto G0 , G1
End If
End_prog:
End

L0:
Print "0 entered"
Return

L1:
Print "1 entered"
Return

L2:
Print "2 entered"
Return

G0:
Print "P1 = 0"
Goto End_prog

G1:
Print "P1 = 1"
Goto End_prog
</source><br/>{{Languages}}

[[Category:BASCOM Language Reference]]