Low speed communication between two pic16f's

[fisyon]

hi,
i want to send 3 bytes from pic16f628a to pic16f877a (by hardware serial if possible)
628a running on 32768hz crystal and 877a is on 20Mhz.

my code for 628a:

#chip 16F628a, 0.032768
#config Osc=LP, BODEN=off, WDT=off
#define UART_BAUD_RATE 150
#define TestLed Portb.6

dim Ticks as bit
dim Hours as byte
dim Mins as Byte
dim Secs as Byte



InitTimer0 osc, PS0_32
on interrupt timer0overflow call t0ov
StartTimer 0

'main
  do
    if ticks=1 then
      if Secs<59 Then
          Secs+=1
        Else
          Secs=0
          if Mins<59 Then
            Mins+=1
          Else
            Mins=0
            if Hours<23 Then
              Hours+=1
            Else
              Hours=0
            end if
          end if
        end if

      ticks=0
      set TestLed on
      wait 100 ms
      set TestLed off
      wait 100 ms


        HSerPrint Hours
        HSerPrint Mins
        HSerPrint Secs

      HSerPrintCRLF

    end if


   loop
'end main

sub t0ov
    Ticks=1
end sub

and here for 877a:

#chip 16F877a, 20
#config Osc=HS, BODEN = off, WDT = off

'**********LCD config********
#define LCD_IO 4
#define LCD_DB4 PORTD.4 'LCD pin 11, sematik pin 13, chip pin 27
#define LCD_DB5 PORTD.5 'LCD pin 12, sematik pin 14, chip pin 28
#define LCD_DB6 PORTD.6 'LCD pin 13, sematik pin 15, chip pin 29
#define LCD_DB7 PORTD.7 'LCD pin 14, sematik pin 16, chip pin 30
#define LCD_NO_RW
#define LCD_Enable PORTD.2
#define LCD_RS PORTD.3
#define LCD_BL PORTD.1 'pin 20 LCDBacklight

#define UART_BAUD_RATE 150

Dim Hours as Byte
Dim Mins as Byte
Dim Secs as Byte

'LCD test and startup
cls
set LCD_BL on
print "Test"
wait 1 s
set LCD_BL off
cls
'*******************
On Interrupt UsartRX1Ready call Getting

'Main loop
Do
  Locate 0,0
    Print Hours
  Locate 0, 2
    print ":"
  Locate 0,5
    print Mins
  Locate 0,6
    Print ":"
  Locate 0,7
    Print Secs
wait 100 ms
set LCD_BL off
Loop
'End Main

Sub Getting

cls
    set LCD_BL on
    HSerReceive (Hours)
    HSerReceive (Mins)
    HSerReceive (Secs)
end sub

i got this result on the LCD and it is not changing
0: 0:4

so, is it possible communication by using these speeds over hardware serial? or what can i use for sending and receiving minimum 3 bytes per second?

[William Roth]

Hi,

HerPrint sends a string of ASCII data , Example: < HserPrint 44 > will send 2 bytes, each with a value of 52 since 52 is the value for the character "4" .

Try using "Hsersend" instead of HserPrint for sending byte data.

[fisyon]

Thanks for the correction. still not working...
i figured out i got this result from 877a without connecting the other.
how can i test if it is senders fault or receivers fault?
Edit:
seems "on interrupt UsartRX1Ready call ..." is not triggered...

[William Roth]

Seems you have misspelled "USART" With UART

And you need to enable USART blocking. Should look like this:

#define USART_BAUD_RATE 150
#define USART_BLOCKING
#define USART_TX_BLOCKING

[viscomjim]

I've been trying to figure this out too and for some reason I can wrap my head around the difference between hsersend and hserprint. From the manual...

HSerPrint is used to send a value over the serial connection. user_value can be a string, integer, long, word or byte.

HSerSend - This command will send a byte given by user_byte using the hardware RS232 module.

Can someone with a better understanding spell out when to use one over the other? Maybe it's just me, but can't a byte be a string value, or integer too? Not getting it yet, sorry. Is HSerPrint better for certain things when trying serial communication? Again, sorry for not getting it...

Thanks in advance!!!!

I have to Edit this post real quick, I have to say that GCB is incredible. Even though I am still learning, I can't believe how much you can do using this awesome FREE piece of work. I am truly thankful to all of the contributors for this. It is hard to believe that so much effort is given away for free for others to accomplish things that would not be done if it were not for others selfless efforts. I am not a wordsmith, thats for sure... but you get the point.

[fisyon]

@William Roth
it was not misspelling.
i tried "USART" before but i got this error:

Error: USART baud rate is too low

edit: just tested for the minimum value: 1221...

[fisyon]

yet, can't figure out how to send and receive 3 bytes over serial. i think i need to create a buffer or something like that which i don't know "how" either...

so, i thought to send these three bytes by converting and joining into a string variable.
then i tried to write something like this:
...
dim mystring as string
...
mystring = Str(Hours) + ":" + Str(mins) + ":"............

SynWrite crashed before writing that line...
i thought that is just a coincidence. but next time at this line SynWrite crashed again...
please, can someone confirm this? (bug?)

i think this is not a success even if i can send and receive this 3 bytes in a string form, because this will be unneccesary long way for a simple(!) task.

ps: maximum baud rate setting without getting compiler error for 32768hz crystall is 2048.

[William Roth]

You do NOT Need a buffer. You just need to get code set up properly and then do methodical testing/troubleshooting if things do not work as expected. Test one code section at a time instead of the entire program. When a section is working move to the next. When that is working add both together and retest. Then move to the next ... and so on.

I think you have several issues. I can get it your code working here just fine at 150 Baud with a 32KHz Crystal, using a PIC16F886. The 886 has the same USART and oscillator block as your 16F628a. I DO NOT get "baud too low" messages when I change the PIC to 16F628a and compile.

With my setup the external Oscillator works. The interrupt works. And the three data byte are sent correctly at the correct baud as confirmed with a logic analyzer. So why does yours not work ?

First, confirm that the 628A is actually operating on the crystal and not falling back to the internal oscillator. If it falls back to the internal oscillator then nothing will work becasue all timing will be incorrect. Do this with a simple program that flashes the LED ON/OFF every second. Does it work as expected or does the LED come on and stay on? If not as expected then the crystal is not operating.

Use this exact code. Do not change it in any way.

#chip 16F628a, 0.032768
#config OSC=LP, BOREN=off, WDT=off, FCMEN = OFF
#define TestLed Portb.6
DIR PORTB.6 OUT

Do
 Set TestLED ON
 Wait 1 s
 Set TestLED OFF
 Wait 1 S
Loop

If this does not flash the LED on 1 sec, and off 1 sec then the external crystal is not working. did you use loading capacitors ? What values? .

If this code works as expected then let me know and I will provide you more working code.

[William Roth]

I do not get baud rate too low messages. So I need to see the exact code that produces this message and I need to know what version of the GCB compiler you are currently using.

If you are not using the latest version of GCB .(97.01) then the first thing you need to do is update.
.

[fisyon]

hello William,
it is a bit difficult to test step by step both circuits.
however i am sure the external oscillator of 628a (32768hz) working as expected. if you look again at first post you can see my TestLed setup. it blinks...

for the baud rate setup; i think i confused you:

for 32khz (628a) i can not compile higher than 2048.
here is the full message when i try to compile with 2049 baud:

14:15:52 G+Stool-COMPILE/ASSEMBLE, processing E:\PIC\GCB@Syn\G+Stools\makeHEX.bat
Source-File = E:\PIC\pic16f628aSerialOSCtest.gcb
5.3 Sec. <<< WARNINGs / ERRORs while compiling!
Doubleclick on errormessage below to go to sourcecode-line:
usart.h (363): Error: Cannot store -1 in the byte variable SPBRG

for 20mhz (877a) i can not compile lower than 1221.
here is the full message when i try to compile with 1220 baud:
14:13:46 G+Stool-COMPILE/ASSEMBLE, processing E:\PIC\GCB@Syn\G+Stools\makeHEX.bat
Source-File = E:\PIC\pic16f877ALCDPortDSerialReceiver.gcb
6.7 Sec. <<< WARNINGs / ERRORs while compiling!
Doubleclick on errormessage below to go to sourcecode-line:
Error: USART baud rate is too low

so i decided to make it 2048 for both chips.
it seems somewhat works. but i got some strange output like:
5: 0 :6
then a few seconds later:
10 : 0 :11
17: 0 :18
22: 0 :23
...

then a few minutes later it stays on this:
00

my gcbasic version is 0.97.1. it is the last version as far as i know.

ok, let me add my latest codes for both chips:

#chip 16F628a, 0.032768
#config Osc=LP, BODEN=off, WDT=off
#define USART_BAUD_RATE 2048
#define TestLed Portb.6

dim Ticks as bit
dim Hours as byte
dim Mins as Byte
dim Secs as Byte

InitTimer0 osc, PS0_32
on interrupt timer0overflow call t0ov
StartTimer 0

'main
  do
    if ticks=1 then
      if Secs<59 Then
          Secs+=1
        Else
          Secs=0
          if Mins<59 Then
            Mins+=1
          Else
            Mins=0
            if Hours<23 Then
              Hours+=1
            Else
              Hours=0
            end if
          end if
        end if

      ticks=0
    set TestLed on
      wait 100 ms
    set TestLed off
      wait 100 ms


        HSerSend Hours
        HSerSend Mins
        HSerSend Secs

    end if


   loop

sub t0ov
    Ticks=1
end sub

and for the "receiver" side:

#chip 16F877a, 20
#config Osc=HS, BODEN = off, WDT = off

'**********LCD config********
#define LCD_IO 4
#define LCD_DB4 PORTD.4 'LCD pin 11, sematik pin 13, chip pin 27
#define LCD_DB5 PORTD.5 'LCD pin 12, sematik pin 14, chip pin 28
#define LCD_DB6 PORTD.6 'LCD pin 13, sematik pin 15, chip pin 29
#define LCD_DB7 PORTD.7 'LCD pin 14, sematik pin 16, chip pin 30
#define LCD_NO_RW
#define LCD_Enable PORTD.2
#define LCD_RS PORTD.3
#define LCD_BL PORTD.1 'pin 20 LCDBacklight

#define USART_BAUD_RATE 2048
#define USART_BLOCKING
#define USART_TX_BLOCKING

Dim Hours as Byte
Dim Mins as Byte
Dim Secs as Byte

'LCD test and startup
cls
set LCD_BL on
print "USART saat okuma"
wait 1 s
set LCD_BL off
cls
'*******************
On Interrupt UsartRX1Ready call Getting

'Main loop
Do
  Locate 0,0
    Print Hours
  Locate 0, 2
    print ":"
  Locate 0,5
    print Mins
  Locate 0,6
    Print ":"
  Locate 0,7
    Print Secs
wait 100 ms
set LCD_BL off
Loop


Sub Getting

    set LCD_BL on
    HSerReceive (Hours)
    HSerReceive (Mins)
    HSerReceive (Secs)
    cls
end sub

There is no compiler error for both at 2048 baud.
the TestLED on 628a (portB.6) and backlight of 877a's LCD, both blinks (not synchronised)

[mmotte]

Greetings fisyon,

If you look on the PIC16F877a datasheet table 10-3 the lowest baud is 1200 but the SPBRG is at 255 which must be the limit. i can't get your code to compile at 1200 but it does at 2400.

If I change the chip to PIC16F887 at 20mhz then you code compiles down to 300 baud. Must be some difference in the microcontroller. I'll llook further to see what the difference is.

Your implementing a clock on the second chip '628a. Why don't you implement it on the '877a using timer 1 and a external 32728 crystal on RC0 and RC1? This would eliminate the comm problem and a chip.

BR
M

[mmotte]

Greetings viscomjim,

Serial communication is a byte at a time.
HSerSend takes the byte that your are sending and sends it to the correct USART transmit register. HSerSend doesn't care if your byte is a number or an ascii character. On some PICs or AVRs there can be more than one USART.

HSerPrint converts a byte, word, long or string to the ascii represenation and sends it using the HSerSend command. HSerPrint's ability to accept different varaible types is called "overloading" which is programming jargon.This conversion is a multistepped process.

For numbers, the number is taken apart and converted to to the ascii characters.
248 / 100 = 2 , 2+48 = 50 , 50 is sent using HserSend
48/10 =4 , 4 +48 =52 , 52 is sent using HSerSend
8 is left , 8 + 48 = 56 , 56 is sent

For Strings, The chars are already assumed to be ascii.
MyString(0) has the length of the string in.
So a simple For loop is set up from 1 to the print length which is MyString(0) .

MyString(1) is sent to HSerSend
MyString(2) is sent to HSerSend
....
until Print Length is achieved.

BR
M

[fisyon]

@mmotte

Why don't you implement it on the '877a using timer 1 and a external 32728 crystal on RC0 and RC1?

my goals are:

to build a modular design. (i can attach / detach both of them easily right now)
low power, battery backed RTC.
to learn serial communication.
plus, i can use 877a for faster jobs (for example: driving six digits of 7 segment display)

PS:

so, i thought to send these three bytes by converting and joining into a string variable.
then i tried to write something like this:
...
dim mystring as string
...
mystring = Str(Hours) + ":" + Str(mins) + ":"............
SynWrite crashed before finishing this line...
i thought that is just a coincidence. but next time at this line SynWrite crashed again...
please, can someone confirm this? (bug?)

i am using GCBasic 0.9.0.1 and SynWrite 6.22.2290 on windows 8.1.
may you try to duplicate that crash?

[William Roth]

This is not supported/allowed and will return a compiler error ..

 mystring = Str(Hours) + ":" + Str(mins) + ":"

.
.
.
This works Ok

  MyString = Str(hours)
  MyString = MyString + ":" + Str(mins)

The IDE did not "crash" on the error with my systems (Win7/Win10) so I am guessing the crash is specific to Win8.1 or to your system.

When you say Synwrite crashes, what specifically do you mean ? Does the entire IDE crash? Is there an error message? If so what does it say ? Can you provide a screenshot ?

[fisyon]

The message is ~:
SynWrite for Great Cow Basic has stopped working
A problem caused the program to stop working bla bla...

to click the button on the message box will close SynWrite.

You can see my crasher line in the background.

may you try to write this line without spaces? mystring = Str(Hours)+":"+Str(mins)+":"+Str(secs)+":"
i know, this is not a good style even if compiled successfuly...

btw: i have "windows8.1 single language" (turkish) on my laptop...

[Anobium]

This is a Synwrite issue. Edit your source file in Notepad, remove any odd characters and save. I have seen this myself and I was unable to determine the root cause of the issue.

So, open in Notepad, remove any odd characters, save, and reopen in IDE.

[fisyon]

finally i have some progress:
256 baud looks like working for sender (628a) side.
i tested it by an arduino with a software serial example.

now, i think i need a software serial for the receiver (877a) side because 20Mhz is too fast for 256 baud.

is there a low baud rate limit for software serial?

@Anobium, i know it is SynWrite's bug, not the GCBasic's.

[fisyon]

my chips are communicating successfuly with each other, thank you all.

however, when i am trying to display time on a 6x 7 segment CC display i can get and show the bytes but the code waits at the "Ser1Receive" line. the display goes off for ~half a second at that line.

defining "SER1_RXNOWAIT off" reduces/eliminates that pause but it causes corrupted or no data.

i know, my baud rate is too low and i can't increase because of low crystall speed.

is there a trick or should i give up ?

[William Roth]

Perhaps you should consder using a higher clock speed and higher baud rate on the 628a. There are other ways to get an accurate 1 sec time base than using a 32.768 KHz clock crystal.

You could also implement a non blocking backround serial receive on the 877.

Why does the 628a even need to calculate the time and send serial data? You could have the 628a simplysend a short pulse every1sec to the 877 and then let the 877 do the rest.

[fisyon]

i want to build 628a as a RTC. i am planning to operate it by batteries. i thought that kind (low speed) of operation will consume less power. i also want to keep time against power loss. that is why i am stuck with this setup.
anyway, i think i have to give up with the smooth display idea with this design.