Tiny software serial transmitter ported to PIC

[Frank Steinberg]

Hi

I ported the Tiny-Software-Transmitter to PIC MC. The attached sample realizes a software UART (in fact ist an 'AT', because ist neither Universal nor a Receiver but an RS232 Asynchron Transmitter).

Tiny means, there are only 24 words (!) added to the hex to be able to send a byte.
- 13 lines of assembler code
- no timers are used
- no other hardware modules are used
- no interrupt is used
- 9600 - 128000 baud are possible at 16 Mhz
- 8N1 format only
- Tx-Pin is user configurable

Because I'm new to ASM I need some help. The code works for me on a PIC12f1501 an a PIC18f13k50. But it lacks on 'bank selection' and 'page selection' in the asm code. Can that be a problem, if the code would be inserted in another (more complex) program? How can this be fixed? If I try to add 'banksel' in the code, GCB generates an error - why?

Frank

The sample:

'''A demonstration program for GCB  - PIC only -
'''---------------------------------------------------------------------------------
'''This program is a super slim software serial transmitter (151 words on a PIC12f1501)
''' realized with 13-line asm code, PIC-Assembler so it's PIC only
''' tested up to 128000 baud on a 16 Mhz PIC 12f1501
'''The pulse polarity ist designed for TTL-USB-Serial-Converters,
''' to invert, switch bcf / bsf (... TTX_PORT,TTX_PIN) in TTxSendByte
'''
'''@author  Frank Steinberg guided by the code of Ralph Doncaster:
''' http://nerdralph.blogspot.de/2013/12/writing-avr-assembler-code-with-arduino.html
'''@licence GPL
'''@version 1.0
'''@date    21.12.2016
'''********************************************************************************

; ----- Configuration
#chip 12F1501, 16
#config LVP = Off
#option Explicit
'OSCCON = b'01011010'     'set internal oscillator to 1 Mhz
'OSCCON = b'01110010'     'set internal oscillator to 8 Mhz
 OSCCON = b'01111010'     'set internal oscillator to 16 Mhz

; ----- Define Hardware settings
;       Config Tiny Software Tx:
;        calculate delay-counter: TTX_DELAY=((CPUFrequency/4/BaudRate)-11)/3)
;         16Mhz: 7=128000 8=115200 19=57600 31=38400 43=28800 66=19200 135=9600
;          1Mhz: 5=9600 31=2400
#define TTX_DELAY 8       '115200 baud
#define TTX_PORT PORTA    'use this port to send serial data
#define TTX_PIN 2         'use this pin to send serial data
Dir TTX_PORT.TTX_PIN Out  '... and make it output
Set TTX_PORT.TTX_PIN On   'set HIGH to make the first startbit recognizable

; ----- Variables
Dim xx As Byte
xx = 48                     'begin with a 0
Dim TTxSVar As String * 20  'create a string

; ----- Main body of program commences here.

 Do Forever

  TTxSendByte(13)   'new line in Terminal
  TTxSendByte(10)
  TTxSendByte(">")
  TTxSendByte(xx)   'send an alternating byte
  TTxSendText(" TinyTx Software Transmitter ")    'send the text
  'TTxSVar = Str(xx) 'Str(xx) adds 278 byte code!
  'TTxSendString
  xx += 1           'alternate byte
  Wait 1 s          'time to enjoy the result

 Loop       'jump back to the start of the program


Sub TTxSendText (In TTxText) 'Send given text bytewise

  Dim TTxText As String * 20 'create a string
  Dim ii As Byte

  For ii = 1 To TTxText(0)   'first byte in array is the string-length
   TTxSendByte(TTxText(ii))  'send via subroutine
  Next

End Sub


Sub TTxSendString  'Send string >TTxSVar< bytewise

  Dim ii As Byte

  For ii = 1 To TTxSVar(0)   'first byte in array is the string-length
   TTxSendByte(TTxSVar(ii))  'send via subroutine
  Next

End Sub


Sub TTxSendByte (In TTxDataByte)  'serial out one byte (8 databit, no paritybit, 1 stopbit)

   Dim TTxDlyCnt, TTxBitCnt As Byte

   TTxBitCnt = 10          ;10 bits to transmit (1 start + 8 data + 1 stop)
   bcf STATUS,C            ;clear CarryFlag to 0 (needed for startbit LOW)

  TTxLoop:
    btfss STATUS,C         ;skip next line if CarryFlag=1
    bcf TTX_PORT,TTX_PIN   ;set pin LOW if CarryFlag=0
    btfsc STATUS,C         ;skip next line if CarryFlag=0
    bsf TTX_PORT,TTX_PIN   ;set pin HIGH if CarryFlag=1

    TTxDlyCnt = TTX_DELAY  ;number of delay-loops
    decfsz TTxDlyCnt,1     ;decrement delaycounter, skip next line if 0
    GOTO $-1               ;loop to line above until delaycounter=0

    bsf STATUS,C           ;set CarryFlag to 1 (fills databyte with 8*1 - needed for stopbit HIGH)
    rrf TTxDataByte,1      ;shift next bit to CarryFlag
    decfsz TTxBitCnt,1     ;decrement bitcounter, skip next line if 0
  GOTO TTxLoop             ;process next bit until bitcounter=0

End Sub

[Anobium]

Good code, Frank. Really nice.

Do not struggle with banksel - simply mix ASM and Great Cow BASIC.
You assign a variable. Use GCB assignment. GCB will sort out pages andg banks.
You need a goto. Use GCB goto. GCB will sort the correct addressing across all the chips.

[Frank Steinberg]

Thank you for the answer.

You assign a variable. Use GCB assignment. GCB will sort out pages andg banks.

I wonder if is's really ruled out, that GCB adds a 'banksel'. In this case the asm code won' t work anymore, because the jumps are only to the next line. I could handle that by adding goto-jumps to labels !? But that is extra code an slows it down (slightly).

You need a goto. Use GCB goto. GCB will sort the correct addressing across all the chips.

How can I force that; it's the same command?

Frank

[Anobium]

@Frank. Which piece of code are we trying to optimise? i can try here over the Holiday period.

[Anobium]

It is the Holiday period. :-)

[Frank Steinberg]

It is the Holiday period. :-)

You lucky one!
I am filled with family and Christmas obligations until the 26th.

Ideas for the next steps:

• creating compatible code for IC and AVR
• finding a smart way to detect the interrupt status (enabled or not) to restore it after sending a byte
• to do the baud calculation by a script
• creating a proper GCB library

That's my last code, so the first step is mostly done (hopefully)

'''A demonstration program for GCB  - PIC only -
'''---------------------------------------------------------------------------------
'''This program is a super slim software serial transmitter (151 words on a PIC12f1501)
''' realized with 13-line asm code, PIC-Assembler so it's PIC only
''' tested up to 128000 baud on a 16 Mhz PIC 12f1501
'''The pulse polarity ist designed for TTL-USB-Serial-Converters,
''' to invert, switch bcf / bsf (... TTX_PORT,TTX_PIN) in TTxSendByte
'''
'''@author  Frank Steinberg guided by the code of Ralph Doncaster:
''' http://nerdralph.blogspot.de/2013/12/writing-avr-assembler-code-with-arduino.html
'''@licence GPL
'''@version 1.0
'''@date    24.12.2016
'''********************************************************************************

; ----- Configuration
#chip 12F1501, 16
#config LVP = Off
#option Explicit
'OSCCON = b'01011010'     'set internal oscillator to 1 Mhz
'OSCCON = b'01110010'     'set internal oscillator to 8 Mhz
 OSCCON = b'01111010'     'set internal oscillator to 16 Mhz

; ----- Define Hardware settings
;       Config Tiny Software Tx:
;        calculate delay-counter: TTX_DELAY=((CPUFrequency/4/BaudRate)-13)/3)
;         16Mhz: 6=128000 7=115200 19=57600 31=38400 43=28800 66=19200 135=9600
;          1Mhz: 5=9600 31=2400
#define TTX_DELAY 6      '115200 baud
#define TTX_PIN PORTA.2  'use this pin to send serial data
Dir TTX_PIN Out          '... and make it output
Set TTX_PIN On           'set HIGH to make the first startbit recognizable

; ----- Variables
Dim xx As Byte
xx = 48                     'begin with a 0
Dim TTxSVar As String * 20  'create a string

; ----- Main body of program commences here.

 Do Forever

  TTxSendByte(13)   'new line in Terminal
  TTxSendByte(10)
  TTxSendByte("T")
  TTxSendText("inyTx Software Transmitter: ")  'send a text
  TTxSendByte(xx)   'send an alternating byte
  'TTxSVar = Str(xx) 'Str(xx) adds 278 byte code!
  'TTxSendString
  xx += 1           'alternate byte
  Wait 1 s          'time to enjoy the result

 Loop       'jump back to the start of the program


Sub TTxSendText (In TTxText) 'Send given text bytewise

  Dim TTxText As String * 20 'create a string
  Dim ii As Byte

  For ii = 1 To TTxText(0)   'first byte in array is the string-length
   TTxSendByte(TTxText(ii)) 'send via subroutine
  Next

End Sub


Sub TTxSendString  'Send string >TTxSVar< bytewise

  Dim ii As Byte

  For ii = 1 To TTxSVar(0)   'first byte in array is the string-length
   TTxSendByte(TTxSVar(ii))  'send via subroutine
  Next

End Sub


Sub TTxSendByte (In TTxDataByte)  'serial out one byte (8 databit, no paritybit, 1 stopbit)

  Dim TTxDlyCnt, TTxBitCnt As Byte

  TTxBitCnt = 10           ;10 bits to transmit (1 start + 8 data + 1 stop) [GCB]
  bcf STATUS,C             ;clear CarryFlag to 0 (needed for startbit LOW) [ASM]

  TTxLoop:
    ;9 cycle loop + delay per byte
    btfsc STATUS,C         ;skip next line if CarryFlag=0 [ASM]
   goto  TTx1              ;goto TTx1 if CarryFlag=1
    Set TTX_PIN Off        ;set pin LOW if CarryFlag=0 [GCB]
  TTx1:
    btfss STATUS,C         ;skip next line if CarryFlag=1 [ASM]
   goto  TTxDone           ;goto TTxDone if CarryFlag=0
    Set TTX_PIN On         ;set pin HIGH if CarryFlag=1 [GCB]
  TTxDone:
    TTxDlyCnt = TTX_DELAY  ;number of delay-loops [GCB]
  TTxDelay:
    ;delay-loop = (x cycle * delaycounter) -1
    decfsz TTxDlyCnt,F     ;decrement delaycounter, skip next line if 0 [ASM]
   goto TTxDelay           ;loop to TTxDelay until delaycounter=0
    bsf STATUS,C           ;set CarryFlag to 1 (fills databyte with 8*1 - needed for stopbit HIGH)[ASM]
    rrf TTxDataByte,F      ;shift next bit to CarryFlag [ASM]
    decfsz TTxBitCnt,F     ;decrement bitcounter, skip next line if 0 [ASM]
   goto TTxLoop            ;process next bit until bitcounter=0

End Sub

... and for AVR:

'''A demonstration program for GCB  - AVR only -
'''--------------------------------------------------------------------------------------------------------------------------------
'''This program is a super slim software serial transmitter (322 bytes flash)
''' realized with 15-line asm code, AVR-Assembler so it's AVR only
''' tested up to 256000 baud on an 16 or 16.5 Mhz attiny85 (digispark)
'''The pulse logic ist designed for TTL-USB-Serial-Converters,
''' to invert, switch On / Off in Line 66 & 69 (Set TTX_PIN ...)
'''
'''@author  Frank Steinberg with the largest portion of Ralph Doncaster:
''' http://nerdralph.blogspot.de/2013/12/writing-avr-assembler-code-with-arduino.html
'''@licence GPL
'''@version 1.0
'''@date    24.12.2016
'''********************************************************************************

; ----- Configuration
#chip tiny85, 16       'intended for digispark board
#option Explicit

; ----- Define Hardware settings
;       Config Software Tx:
;       [ calculate delay-counter: TTX_DELAY=((CPUFrequency/BaudRate)-9)/3) ]
#define TTX_DELAY 17     '16.5Mhz: 17=256000 19=230400 44=115200  '1Mhz: 5=38400 135=2400
#define TTX_PIN PORTB.3  'use this port to send serial data
Dir TTX_PIN Out          '... and make it output
Set TTX_PIN On           'set HIGH to make the first startbit recognizable

; ----- Variables
Dim TTxSVar As String * 20  'create a string
Dim xx As Byte
xx = 48                     'begin with a 0

; ----- Main body of program commences here.

 Do Forever

  TTxSendByte(13)   'new line in Terminal
  TTxSendByte(10)   '
  TTxSendByte("T")  'this is a valid byte too
  TTxSendText("inyTx Software Transmitter: ")  'send a text
  TTxSendByte(xx)   'send an alternating byte
  'TTxSendByte(9)    'Tab
  'TTxSVar = Str(xx) 'this adds 564 byte code!
  'TTxSendString     'this adds 2 byte code
  xx += 1           'alternate byte
  Wait 1 s          'time to enjoy the result

 Loop


Sub TTxSendText (In TTxText)  'Send given text bytewise

  Dim TTxText As String * 20  'create a string
  Dim ii As Byte

  For ii = 1 To TTxText(0)    'first byte in array is the string-length
   TTxSendByte(TTxText(ii))   'send via subroutine
  Next

End Sub


Sub TTxSendString  'Send string >TTxSVar< bytewise

  Dim ii As Byte

  For ii = 1 To TTxSVar(0)   'first byte in array is the string-length
   TTxSendByte(TTxSVar(ii))  'send via subroutine
  Next

End Sub


Sub TTxSendByte (In TTxByte)  'serial out one byte (8 databit, no paritybit, 1 stopbit)

  'cli                   ;disable interrupts
  push R24              ;save register content to stack
  push R25              ;
  push R26              ;
  lds R24, TTxByte      ;load data-byte to register
  ldi R25, 10           ;load number of bits to register (1 start + 8 data + 1 stop)
  com R24               ;invert bits and set carry
  TTxLoop:
    ;9 cycle loop + delay per byte
    brcc TTx1           ;jump to TTx1 if CarryFlag=0
    Set TTX_PIN Off     ;set pin LOW if CarryFlag=1 (translated by GCB to ASM: cbi ...)
  TTx1:
    brcs TTxDone        ;jump to TTxDone if CarryFlag=1
    Set TTX_PIN On      ;set pin HIGH if CarryFlag=0 (translated by GCB to ASM: sbi ...)
  TTxDone:
    ldi R26, TTX_DELAY  ;load delaycounter to register
  TTxDelay:
    ;delay-loop = (3 cycle * delaycounter) -1
    dec R26             ;decrement delaycounter
    brne TTxDelay       ;loop to TTxDelay until delaycounter=0
    lsr R24             ;shift next bit to CarryFlag
    dec R25             ;decrement bitcounter
    brne TTxLoop        ;jump to TTxLoop and transmit next bit until bitcounter=0
  pop R26               ;restore register content from stack
  pop R25               ;
  pop R24               ;
  'sei                   ;enable interrupts

End Sub

Merry christmas to all