AVR-Chat

Not that I disagree with you, however, look at the RETI for th 8051. Also, 
check out the RET and RETI instruction explanantion is the instruction set 
manual. Both of the latter use the same stack operation implying they 
function the same. RET returns to the instruction following the CALL, RETI 
does not.

I've changed my code to accomodate the RETI. Doesn't make much sense to have 
infinite loops.

RETI (80C51 Instruction Set)

Function: Return from interrupt

Description: RETI pops the high- and low-order bytes of the PC successively 
from the stack and restores the interrupt logic to

accept additional interrupts at the same priority level as the one just 
processed. The Stack Pointer is left

decremented by two. No other registers are affected; the PSW is not 
automatically restored to its pre-interrupt

status. Program execution continues at the resulting address, which is 
generally the instruction immediately after

the point at which the interrupt request was detected. If a lower- or 
same-level interrupt was pending when the

RETI instruction is executed, that one instruction is executed before the 
pending interrupt is processed.

Example: The Stack Pointer originally contains the value 0BH. An interrupt 
was detected during the instruction ending at

location 0122H. Internal RAM locations 0AH and 0BH contain the values 23H 
and 01H, respectively. The

following instruction

----- Original Message ----- 
From: "Volkmar Dierkes" <avrfreaks@dierkes.info>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, August 23, 2005 12:50 AM
Subject: [AVR-Chat] Re: mega 168


Dennis,

I am sorry, but you are wrong. In an interrupt driven system, an
interrupt may occur at any time. If the serving of the interrupt
would end in returning to a different address, the code wouldn't be
executed in the desired sequence. If you want to wait in a loop
until the interrupt is being serviced, you need to set a flag in the
ISR and check this flag in your loop to exit it at the given time.

Please reread the datasheet to understand the interrupts correctly.

Volkmar

On Sun, 21 Aug 2005 21:45:48 -0500, Dennis wrote:

> What I am saying is the next instruction is not being executed. In an
> interrupt driven system, a loop is waiting for the interrupt. When it
> happens the process continues from the instruction following the loop. It
> doesn't go back to the loop, or not supposed to.
> D
> ----- Original Message ----- 
> From: "Larry Barello" <yahoo@barello.net>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Sunday, August 21, 2005 9:33 PM
> Subject: RE: [AVR-Chat] mega 168
>
>
>> If what you are saying is true (and it isn't) then this very common
>> programming idiom won't work since an interrupt on the "rjmp" instruction
>> will cause it to exit.
>>
>> Forever:
>> Rcall DoThisTask
>> Rcall DoThatTask
>> Rcall etc
>> Rjmp forever
>>
>> Please re-read my previous response again.  What is pushed is the address
>> of
>> the next instruction to execute, not the next address.
>>
>> Cheers!
>>




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