newbie with serial com question...

I am a newbie, to say the least, to pic programming. I have a bit of vb software that i would like to use to control simple outputs on a pic. I believe the application is commonly referred to as a relay controller. I don't really need design help, moreover serin command help. I am using an example from http://www.rentron.com/PIC16F84.htm. I'll be using a PIC16F871.
Here's some of the code...

INCLUDE "bs2defs.bas"
DEFINE OSC 20
address VAR b2 'board number storage variable
relay VAR b3 'relay number storage variable
stat VAR b4 'relay status ON/OFF variable
serpin VAR porta.0 'serial input pin
trisa = %00000001
trisb = %11111111
trisc = %00000000
trisd = %00000000
trise = %00000000
addr = portb

If address = addr Then
SERIN serpin,N9600,board,relay,stat
SELECT CASE relay
CASE 1
IF stat = 1 THEN HIGH PORTA.1
LOW PORTA.1
CASE 2
IF stat = 1 THEN HIGH PORTA.2
LOW PORTA.2
CASE 3
IF stat = 1 THEN HIGH PORTA.3
LOW PORTA.3
CASE 4
AND SO ON.....

My question is in regards to the use of portb as the 8 bit address for the pic itself. I would like to send a command from the pc to the pic similar to:

MSComm1.Output = address + relay + stat

I would like the pic to allow further processing only upon matching the portb status to the incoming address. Wow, I hope I explained that well enough!?
My goal is to have a few of these boards on the same serial bus, and be able to address each output individually. Well, hopefully one of you gurus can steer me in the right direction.

Thanks to all,
Chris

Hi,

As far as I understood you want to have a network of PICs on a common drop down serial bus and address them on specific requests . So your protocol may be a simple two byte thing, the first byte mentioning which PIC and the second what to do actually. Well if you are putting a DIP switch on a portb and using your entire portb as inputs then you can compare it with incoming address. In all PICs the ports are memory mapped registers so you can do a read directly.

So as you did, It should work, like:

IF incoming_address = portb then

or you can have your own byte variable

myvariable = portb

Then compare or process your variable.

You described it exactly! As far as the code I posted, does it look like it should do what you described, or did I miss something?

Thanks again,
Chris

maybe this one may help
http://www.picbasic.co.uk/forum/showthread.php?t=1192

Thank you guys for the responses you gave me. I'm sorry I couldn't thank you sooner...been busy trying picbasic. I've got one more question, that I hope one of you can help me with. I can't seem to get my head around how the pic can take in three bytes in a row from the PC...

(ie: mscomm1.output = 9 + 22 + 1)

and know that the first byte is the address, the second is the output, and the third is the state? I think I'm just over-thinking this. Can one of you gentleman help me understand this?
Do I do it like this:

serpin VAR porta.0
address VAR b3
output VAR b4
stat VAR b5

If b3 = PORTB then
SERIN serpin,N2400,address,output,stat..........

is serpin b1
is N2400 b2
is address b3
is output b4
is stat b5

Am I thinking correctly, or am I way off base?

Thanks for letting me bend your ear...
Chris

Hi,

Most of the time your PIC should be listening to the available data. Use some sort of acknowledge when it receives a valid packet. You can try respond through the control lines of the RS232 ports.

Other possibilities are using the PIC's hardware USART. The hardware USART normally has a two byte buffer and generates an interrupt when a byte is received.

By using Darrel's Instant Interrupt implementing it should not be a big deal.

All you need to do it get the bytes in a ring array or FIFO for processing later. Use some sort of unique Header and Terminator in your packet send by the PC. If your are using a FIFO in your main program loop go on hunting for the terminator(the last byte received). When found you can check your FIFO's deepest location (since the data packet length is fixed) for a valid header. If found then anything between your header and terminator is your data packet.