Problem with Serin and On Interrupt

[EvilGhozt]

Why doesnt this code work correct?
Pic16f628 @ 4mhz

DEFINE OSC 4
on interrupt goto myint
intcon = %10010000

loop:
pause 1
goto loop

disable
myint:
serin2 portb.1, 396, [wait("IB")]
INTCON.1 = 0
resume
enable

The problem is that when i send "IB" from the computer to the pic it hangs up in the Serin2 myint part and doesnt move along before it receive another "IB". It seems like it miss the first "IB" I sent, and then Serin waits for the computer to send "IB" again... Does the interrput command take to long time so it wont catch the first bit or something?

I'm quite noob and my english sux so please explain it easy ;)



Edit: Sorry i duplicated the post, how do i delete it :P ?

[Darrel Taylor]

Couple of things going on here. First, by using ON INTERRUPT the program can only be interrupted "In-between" PBP statements. With a PAUSE 1, and serial speed of 2400 baud (.4ms per bit), you can easily lose the first 3-bits before the interrupt even occurs.

Second... Even IF you could get to "myint" faster, the start bit is already gone, because that's what would have triggered the interrupt to begin with.

Since you are using a 16F628, it would be better to use the USART. But, if you don't want to do that ...

Send 1 or 2 extra characters before the string you are waiting for to give it time to get to the serin2 statement. i.e. "xxIB"

Also, serin2 mode 396 is 2400 baud, TRUE. Which means that the RS232 signal idles HIGH, so the first bit coming in will be a transition from HIGH to LOW. It may be better to change the INTEDG bit in the OPTION register to 0 so that it interrupts on the "Falling Edge". It defaults to 1. Saves one more "BIT" period.

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[EvilGhozt]

Thx for the reply.

But I think I'm going to use another method.
By connecting RTS to B0/INT I can easy toggle RTS HIGH and then LOW, after that sending the rs232 data. This will alert the pic to listen for any incomming data on RX port...



Now to next problem.

Code:


High led1
Pause 100
Low led1
SerOut2 PORTB.2,396,["Start"]

loop:
i = i + 1
IF i = 1000 Then High led2
IF i = 2000 Then
Low led2
i = 0
EndIF
goto loop

* There are some other code but I dont think its relevant in this matter..

I resently detected that the led2 in main loop does not always start flashing in the beginning (happens about ~ once of ten) . It can take up to 5-6 sec before it starts flashing. Is there some problem with the SerOut2 command? or pic damage?
Some other thing I was wondering, how often those a pic fail? I mean, can I run a loop like that (room temperature ~20C) in a month/year without a fail that cause a brake?

[Darrel Taylor]

By connecting RTS to B0/INT I can easy toggle RTS HIGH and then LOW, after that sending the rs232 data. This will alert the pic to listen for any incomming data on RX port...


WHY? Why not just use the USART and forget about the extra wiring. The USART will generate an interrupt to notify when data comes in. And, it won't miss a BIT.
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[EvilGhozt]

How should I write the code then?
I would be grateful if you could paste some code or just help me with some hints how to do...

Thx mate.

[Darrel Taylor]

Using your original example, it might look like this ...
DEFINE OSC 4

DEFINE HSER_RCSTA 90h 'Hser receive status init
DEFINE HSER_TXSTA 20h 'Hser transmit status init
DEFINE HSER_BAUD 2400 'Hser baud rate

INTCON.6 = 1 ' Enable Peripheral interrupts
PIE1.5 = 1 ' Enable USART receive ints (RCIE)

on interrupt goto myint

loop:
pause 1
goto loop

disable
myint:
Hserin [wait("IB")]
resume
enable

HTH,
&nbsp; Darrel

[EvilGhozt]

Should i connect B0/INT to B1/RX? or does this detect interrupt on the RX port?

[Darrel Taylor]

For a 16F628, the USART pins (RX and TX) are 7 and 8. Same as RB1 and RB2.
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[EvilGhozt]

Oh it works! Thanx _ALOT_ Darrel Taylor.
This will make the program faster and a bit easier. :D

That was all for today, time for bed. Good night...