Serial Communication Problem

[elec_mech]

Upon having another set of eyes look at my code and using the debugger I'm learning to use slowly with more interest, I forgot to clear the counter and i variables. Effectively it was continuing to loop because those variables still had values assigned. Thank you for your time and help Steve, I do appreciate it.

To anyone else who may be interested in receiving a serial string, reading it and then doing something based upon a character(s) received, let me know and I'll post some really nice code to play with.

Thanks again to Joe, Luciano, and Steve. I learned a great deal by all the info and code posted.

[Dalomir]

I put the schematic in the attachement of this post.

Its an usart with 2 PIC18F452 linked together by PIN 25 and PIN 26

One receive a paralelle 4 bits number from a numerical keyboard, light LED at PIN 2, 3, 4, 5, 6, 8, 9 and 10 to show that number and send that number directly to the other PIC RX PIN.

Thats other PIC then receive that serial number and lights LED in the same way as the other PIC, showing that the number was successfully sent.

If anyone has a code that would make it work, I would really appreciate.

[leemin]

To anyone else who may be interested in receiving a serial string, reading it and then doing something based upon a character(s) received, let me know and I'll post some really nice code to play with.

yupe. i need a program to receive a serial string, reading it and then doing something. my string is something like this X-Addr-Mode-Data(30bytes)-Y
where X stand for SOT and Y stand for EOT. Addr is use to indicate the dedicated address value i want to send data.

my code is something like below:
include "modedefs.bas"
DEFINE SHIFT_PAUSEUS 20
define OSC 20
DEFINE HSER_CLOERR 1 ' automatic clear overrun error

TRISA=%11110000
TRISB= %11111011
TRISC.6 = 1
TRISC.7 = 0

symbol Addr_Data_In=porta.4
symbol en=porta.3
symbol stb=porta.2
symbol clk=porta.1
symbol data_out=porta.0

SPBRG = 32 ' Set baud rate to 9600
RCSTA = $90 ' Enable serial port and continuous receive
TXSTA = $24 ' Enable transmit and asynchronous mode
RCIF VAR PIR1.5 ' Receive interrupt flag (1=full , 0=empty)
TXIF VAR PIR1.4 ' Transmit interrupt flag (1=empty, 0=full)
OERR var RCSTA.1 ' Overrun error
CREN var RCSTA.4 ' Continuous receive
ADCON1=6

display: if RCIF then
i=RCREG
if i != "X" then discard

redo: hserin 500,discard,[i]
if i="Y" then discard
serialstring[counter]=i
counter=counter+1
goto redo

discard: if i="Y" then success=1
endif
if success then
cren = 0
if (serialstring[0] <> address_Value) then reset
if serialstring[1] = $30 then turn_off_led
serialstring[2]=a29
serialstring[3]=a28
serialstring[4]=a27
serialstring[5]=a26
serialstring[6]=a25
serialstring[7]=a24
serialstring[8]=a23
serialstring[9]=a22
serialstring[10]=a21
serialstring[11]=a20
serialstring[12]=a19
serialstring[13]=a18
serialstring[14]=a17
serialstring[15]=a16
serialstring[16]=a15
serialstring[17]=a14
serialstring[18]=a13
serialstring[19]=a12
serialstring[20]=a11
serialstring[21]=a10
serialstring[22]=a9
serialstring[23]=a8
serialstring[24]=a7
serialstring[25]=a6
serialstring[26]=a5
serialstring[27]=a4
serialstring[28]=a3
serialstring[29]=a2
serialstring[30]=a1
serialstring[31]=a0
endif
reset: cren=1 ' Enable receiver
goto display

[elec_mech]

I need to sift through my code and pull out the serial stuff (it's a long code as it stands) and reply to you this evening. What PIC are you using by the way?

Also, could you describe what you want to do again in more detail? I'm a little confused when you say X stands for SOT and Y for EOT. I'm still a newbie in programming, but I'm sure I can help you with this. So far I gather you want to receive a serial string and read it. You then want the PIC to do something by way of transmitting another serial string and placing the characters in a specific location along that string? Which is no problem I just want to make sure I'm giving you what you want.

-Tony

[elec_mech]

Okay, I brought this home, tweaked it with a different programmer and when I try to compile it, it says it is unable to "fit variables". I'm think this will work as it stands, but you may find some errors on my part.

In any event, this waits for serial data and once received looks at the first two characters to be sure the string is what you expect it to be. You can take this out if your serial input changes every time (the first two and last two characters in a string). If you ever expect more than 40 bytes on a single serial string be sure to change that in the variable definitions.

The branch command really comes in handy for looking at a single character at a specific location in the string and doing different things instead of using the if command.

Take a look at this and see if it helps. Feel free to ask questions.

-Tony

[elec_mech]

ASII Table - All important to serial comms - Check this out:
http://www.lookuptables.com/

[leemin]

ok. thanks for you all previous help. i can work with the USART interrupt with my code already but now i encounter with a new problem.
im using 16f877a.
i need to receive a string of command from computer. then execute some function after received a valid command. now i need to execute the blinking effect by toggling the enable pin to let the led on and off continuosly untill another set string of command come in and either stop blinking or continue blinking.
but now i found out that the blinking sub-routine is a dead loop. when i continuosly execute the blink function and a new string command come in from computer my firmware will hang there.
any solution for this?
i need you all suggestion.
thanks

[BobK]

Hi Leemin,

It's a great idea to have the micro do as much as possible but sometimes it's necessary to have external hardware do some work to free up the micro to do other things more important. Add a gated pulsing circuit that you only need the micro to turn on and off. This can be a single chip circuit like using a CD4093 or even a CD4060. A CD4060 lets you choose flash rates juct by selecting the appropriate output. These are simple circuits and only require a few discretes to finish the job. Let the micro do the more serious stuff.

BobK