ON VALUE

Action

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

 

 

Syntax

ON var [GOTO] [GOSUB] label1 [, label2 ] [,CHECK]

 

 

Remarks

Var	The numeric variable to test. This can also be a SFR such as PORTB.
label1, label2	The labels to jump to depending on the value of var.
CHECK	An optional check for the number of provided labels.

 

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

 

And value = 2, there is no associated label.

 

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.

 

See Also

ON INTERRUPT

 

 

ASM

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

 

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

Ldi R31, High(ON_1_ * 1)

 

Add zl,r24       ; add value to Z

Adc zh,r25

 

Ijmp        ; jump to address stored in Z

 

ON_1_:

 

Rjmp lbl1       ; jump table

Rjmp lbl2

Rjmp lbl3

 

 

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

 

;##### 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

 

Add zl,r24 ; add to address of jump table

Adc zh,r25

Ijmp        ; jump !!!

 

ON_1_:

Rjmp L1

Rjmp L2

ON_1_EXIT:

 

 

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

 

 

Example

'-----------------------------------------------------------------------------------------
'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

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