Communication between two PicChip

[Charles Linquis]

When I mentioned hardware serial port, I was referring to TxD and RxD. Then you could use HSEROUT and HSERIN. Connect those two lines together on your PIC, and you can communicate at 9600 baud at least, on the internal oscillators.

[lerameur]

I just want to do a very simple communication at first, then I will work on better one. I am using the same code as i used a few ago for a project on mine. It was working fine at the time. I was using a different compiler and different software.
I am trying to re-use that code. Now I have taken THE code I used and just removed the extra stuff in the programming that is not needed ( calculation from a wireless thermometer) here is my sending code:

INCLUDE "modedefs.bas"
OSCCON = %01110000 '8 Mhz
Define OSC 8

CMCON = 7 : ANSEL = 0 : ADCON1 = 7
'/////////////////////////
'// LCD configuration //
'/////////////////////////

DEFINE LCD_DREG PORTA ' Set LCD Data port
DEFINE LCD_DBIT 0 ' Set starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTB ' Set LCD Register Select port
DEFINE LCD_RSBIT 0 ' Set LCD Register Select bit
DEFINE LCD_EREG PORTB ' Set LCD Enable port
DEFINE LCD_EBIT 6 ' Set LCD Enable bit
DEFINE LCD_BITS 4 ' Set LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 2 ' Set number of lines on LCD
DEFINE LCD_COMMANDUS 2500
DEFINE LCD_DATAUS 250
DEFINE CHAR_PACING 2000
pause 500

TRISB = %00000000

count_remain var byte
temperature1 var byte
temperature2 var byte

Mainloop:

temperature1 =11: temperature2 =22
count_remain =44



lcdout $FE,1, "TempC: ", dec (temperature1) , ".", dec2 temperature2," ",$DF,"C"
lcdout $FE,$C0, bin count_remain , ".","F"
pause 400

serout portb.2, n2400,[$55,$55,$55,$55,$aa,temperature1,temperature2,coun t_remain]

lcdout $FE,1 : LCDOUT "second ", dec (temperature2 / 100) , ".", dec2 temperature1," ",$DF,"r"
lcdout $FE,$C0, dec count_remain , ".","23"
pause 400

goto mainloop

end

and here is the receiving code:

INCLUDE "modedefs.bas"
OSCCON = %01110000 '8 Mhz
Define OSC 8

CMCON = 7 : ANSEL = 0 : ADCON1 = 7
'/////////////////////////
'// LCD configuration //
'/////////////////////////

DEFINE LCD_DREG PORTA ' Set LCD Data port
DEFINE LCD_DBIT 0 ' Set starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTB ' Set LCD Register Select port
DEFINE LCD_RSBIT 0 ' Set LCD Register Select bit
DEFINE LCD_EREG PORTB ' Set LCD Enable port
DEFINE LCD_EBIT 6 ' Set LCD Enable bit
DEFINE LCD_BITS 4 ' Set LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 2 ' Set number of lines on LCD
DEFINE LCD_COMMANDUS 2500
DEFINE LCD_DATAUS 250
DEFINE CHAR_PACING 2000
pause 500

ADCON1 = %00100010

encoded11 var word : encoded22 var word : encoded33 var word : encoded44 var word : encoded4 var byte
count_remain var byte :temp var byte


TRISA = %00000001 ' Set PORTA to all output
TRISB = %00001111


Mainloop:
'23

lcdout $FE,1 , "hello ", dec 105," ","C"
lcdout $FE,$C0, "before"
pause 300

waitfor55:
serin portb.2 , n2400 , temp : if temp <> $55 then goto waitfor55

waitforaa:
serin portb.2 , n2400 , temp : if temp <> $aa then goto waitforaa

serin portb.2, n2400, encoded11.HighBYTE : serin portb.2, n2400, encoded11.LowBYTE
serin portb.2, n2400, encoded22.HighBYTE


lcdout $FE,1, "encoded11.HighBYTE", dec encoded11.HighBYTE , ".", dec2 encoded11.LowBYTE
lcdout $FE,$C0, "TempF: ", "-", dec encoded22.HighBYTE , "After"
Pause 300


goto Mainloop

end

the sending code seems to work. but the receiving code seems to be stuck on the first LCDOUT, I guess it does not see the 55 or aa...

k

[Charles Linquis]

That is why you need to use the hardware serial port! If you use SERINx you have to sit and wait for the first transition of the start bit of the first char to come in. If you use HSERIN instead, you could simply test for PIR1.5 (at least that is what it is in the 18Fs). It gets set AFTER the whole byte is received, so in just a few instructions, you can tell if the first byte came in. If that bit isn't set, move on. If it is set, then you know there is a char in the receive buffer, so then you can issue the command HSERIN [dummy]. If Dummy = $55 then you can continue to grab chars. Virtually no overhead, and as long as you give it a
little thought, you don't even need interrupts. It will NEVER lose the first character.

Although I always advocate using interrupts, if you didn't want to mess with them, you could:

Figure out the loop time of your slave device. Then you could do the following:

Main:
GotChars = 0
If PIR1.5 then
Hserin [FirstByte] ;------------ You don't need a timeout here because you already know you have a char
if FirstByte = $55 then
HSERIN 50,NotValid, [STR receivebuffer \numbytes]
GotChars = 1
endif
endif
NotValid:
....rest of program here....

goto main

;------------------------------------------------------------------------------------
And your master -

.....

HSEROUT [$55]

pause (this should equal the length of the slave's program loop + a few mSec)

HSEROUT [whatever you want to send]

.......

[lerameur]

i know what you mean. but why did it work before and now it does not.... i can see from my scope the the same signal is going in the pic.. why the heck doesn't it read it.

K

[Charles Linquis]

Maybe you should try smaller-value pull-up resistors. Although most I2C devices can't sink much current, a PIC can sink 25mA easily. You could use 560 ohm pull-up resistors on each end if you had an extremely noisy environment or long wires.

Also, if your two devices aren't on the same PCB, could there be a difference in GND potential between the two devices?

[lerameur]

and i do have a I have the two breadboards sitting side by side, so maybe 9inch of wire between the two. I added 560ohmpull up resistors but nothing changed from before. and I do have a ground wire between them ..

[lerameur]

WHAT is the best technique to communicatebetween two Pic Chip ??
I2C ? HSEROUT ? .....