Converting HSERIN Data to Number

I'm using USART to pass info from one PIC to another. On the slave PIC, I want to read an incoming data stream which will tell me what PWM duty cycle to set on the slave's CCP module. The format of the data sent is this:

S0D3255~

The first character "S" is the 'sync' character (or start of new transmission); the 2nd is the Chip ID (since there will be a few slaves connected to one Master); third character is what option on the slave is going to change; the 4th character is the number of digits in the adjustment value ("255") and the last character is the termination.

I have an ISR attached to the Rc pin of the USART module on my PIC, so it fires overtime a character comes into the buffer. Here's the ISR:

Code:

---

' ***************************************************************
' [RX_INT - interrupt handler]
' ***************************************************************
GetBytes:
' TODO: Update code to handle AdjVal > 1 character (an array?)

    HSERIN [Serialdata]                    ' Get the serial data (guaranteed here to have at

    IF Serialdata = SyncByte THEN         
        IF SyncRcvd THEN                  ' if it's a Sync byte,
            state = 0                      '  last command was corrupted; reset 'state'
            ERROR = 1                      '  and indicate error
        ENDIF
        SyncRcvd = 1                      '  indicate Sync was rcvd
    ELSE
        IF SyncRcvd THEN
            IF !ForMe THEN                ' if we haven't rcvd the ID
                IF Serialdata = ThisChipID THEN 'and this byte matches the ID
                    ForMe = 1              '    indicate ID rcvd
                ELSE
                    state = 0              '    Not meant for this chip, reset and wait for next msg
                ENDIF                     
            ELSEIF !CmdRcvd THEN
                CmdVal = SerialData
                CmdRcvd = 1
            ELSEIF !LenAdjRcvd THEN
                LenAdjVal = SerialData               
                LenAdjRcvd = 1
                i = 0
            ELSEIF !AdjRcvd THEN
                AdjVal = SerialData
                myArray[i] = AdjVal
                i = i + 1
                If i = ArrayLength THEN
                    AdjRcvd = 1
                ENDIF
            ELSEIF !MsgRcvd THEN
                If SerialData = TxEndChar THEN
                    MsgRcvd = 1
                ENDIF
            ENDIF
        ENDIF
    ENDIF

@ INT_RETURN

---

In the Main loop:

Code:

---

Main:
    IF MsgRcvd THEN GOSUB ProcessCmdAdj    ' Process incomming data
.
.
.
GOT Main

---

And here's where I output the result (using MCSP's Serial Communicator):

Code:

---

'*********** Process received command **************************************
ProcessCmdAdj:
'    varResult = myArray[0]*100 + myArray[1]*10 + myArray[2]

    HSEROUT ["Cmd: ", CmdVal, _  ' send Command, Length of Adjustment & Adjustment value and CR/LF
        ", LenAdj: ", LenAdjVal, " [", DEC LenAdjVal, "]", _
          ", Adj: ", myArray[0], myArray[1], myArray[2], 13, 10]
       
       
        '  ", Adj: ", AdjVal, " [", DEC AdjVal,"]", 13, 10]

    state      = 0              ' indicate CMD & ADJ has been processed

    cmdVal    = 0
    LenAdjVal  = 0
    AdjVal    = 0

    For i = 0 to (ArrayLength - 1) ' clear out array
        myArray[i] = 0
    NEXT i

RETURN

---

I can't figure out how to take the 3 characters stored in myArray and convert it to a numerical 255 value that I can then use to set PWM duty cycle. As you can see from the commented-out line above, I tried multiplying the first 2 characters by 100 & 10, but that just gives garbled results. I know the ISR is building the array properly because the above HSEROUT shows me the correct characters in each item of myArray[].

I've never had to do this kind of math/byte manipulation before, so I'd appreciate help here. The full code for the project is here:

Code:

---

' :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
' Based on Darrel Taylor's example
' http://www.picbasic.co.uk/forum/showthread.php?t=9932&p=65066#post65066
' :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

'  MPASM, LabX-1 , PBP3, Using PIC 16F877A @ 4mHz, 9600 Baud,
'  USART and MAX232 to MCS Serial Communicator on PC

' ***************************************************************
' >>>>>>>>>>>>>>>>>    Slave IC ID: 0    <<<<<<<<<<<<<<<<<<<<<<<
' ***************************************************************

ThisChipID CON "0"

DEFINE OSC 4

DEFINE HSER_RCSTA 90h ' enable serial port,
DEFINE HSER_TXSTA 24h ' enable transmit,
DEFINE HSER_BAUD 9600 ' set baudrate to 9600                 
DEFINE HSER_CLOERR  1 ' automatic clear overrun error 

TRISD  = %00000000    ' D to outputs for the LEDs
TRISC  = %10000000    ' PORTC.7 is the RX input, PORTC.6 is the TX output
ADCON1 = %00001111    ' Set up ADCON1 register no matter what yr doing!!!                     
       
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
INCLUDE "DT_INTS-14.bas"    ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"    ' Include if using PBP interrupts

;-- Place a copy of these variables in your Main program -------------------
;--  The compiler will tell you which lines to un-comment                --
;--  Do Not un-comment these lines                                      --
;---------------------------------------------------------------------------
;wsave  VAR BYTE    $20    SYSTEM      ' location for W if in bank0
wsave  VAR BYTE    $70    SYSTEM      ' alternate save location for W
                                        ' if using $70, comment wsave1-3

' --- IF any of these three lines cause an error ?? ------------------------
'      Comment them out to fix the problem ----
' -- Which variables are needed, depends on the Chip you are using --
wsave1  VAR BYTE    $A0    SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
' --------------------------------------------------------------------------

' ***************************************************************
' ASM Interrupt Definitions
' ***************************************************************

ASM
INT_LIST  macro    ; IntSource,          Label,  Type, ResetFlag?
        INT_Handler  TMR1_INT,      ReloadTMR1,  ASM,  no      ; MUST be first
        INT_Handler  TMR1_INT,      _T1handler,  PBP,  yes
        INT_Handler    RX_INT,        _GetBytes,  PBP,  yes
    endm
    INT_CREATE    ; Creates the interrupt processor
ENDASM

':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'  Variable definition
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

ERROR_LED  VAR PORTD.1            ' rename the LED's
LATE_LED  VAR PORTD.2
HEART_LED  VAR PORTD.0

PORTD = 0

LEDonDELAY CON 4

TxEndChar  CON "~"
SyncByte    CON "S"

i          VAR BYTE

SerialData  VAR BYTE
CmdVal      VAR BYTE
LenAdjVal  VAR BYTE
AdjVal      VAR BYTE
ERRORtime  VAR BYTE
LATEtime    VAR BYTE
HEARTtime  VAR BYTE

state        VAR BYTE       
  SyncRcvd    VAR state.0      ' sync byte received
  ForMe      VAR state.1      ' packet is for this device
  CmdRcvd    VAR state.2      ' command has been received
  LenAdjRcvd  VAR state.3      ' decimal length of adjustment value to follow
  AdjRcvd    VAR state.4      ' adjustment factor has been received
  MsgRcvd    VAR state.5      ' compelte message received
  ERROR      VAR state.6      ' sync received out of order
  LATE        VAR state.7      ' command received before last one was processed

state      = 0                ' Initialize default values

i          = 0

cmdVal    = 0
LenAdjVal  = 0
AdjVal    = 0
serialdata = 0               

ArrayLength CON 3
myArray VAR BYTE[ArrayLength]
varResult VAR BYTE
               
' Example of received command from master chip:
' ============================================
'    SyncByte, Chip Id, Cmd Id, Length of modifier, <modifier>, TxEndChar
'HSEROUT ["S",    "0",    "A",                "3",      "155",    "~"]


;--- Change these to match the desired interrupt frequency -------------------
;--- See http://DarrelTaylor.com/DT_INTS-14/TimerTemplate.html for more Info.
@Freq      = 10                  ; Frequency of Interrupts in Hz
@Prescaler  = 2                  ; Timers Prescaler setting
T1CON = $10                      ; $30 = Prescaler 1:8, TMR1 OFF
; $00=1:1, $10=1:2, $20=1:4, $30=1:8 --  Must match @Prescaler value

' Enable interrupts
@ INT_ENABLE  RX_INT        ; enable USART RX_INT interrupts
@ INT_ENABLE  TMR1_INT      ; enable Timer 1 interrupts
GOSUB StartTimer            ; Start Timer 1

Main:
    IF MsgRcvd THEN GOSUB ProcessCmdAdj    ' Process incomming data

    IF ERROR THEN                          ' if there's been an Error
        HIGH ERROR_LED                    '  Turn ON ERROR LED
        ERROR = 0                          '  reset the error flag
        ERRORtime = LEDonDELAY            '  start countdown till LED-OFF
        HSEROUT ["Error",13,10]
;        HSEROUT ["SyncRcvd: ", DEC SyncRcvd,", SyncIndx: ",DEC SyncIndx, _
;                ", ForMe: ", DEC ForMe,", CmdRcvd: ",DEC CmdRcvd, _
;                ", AdjRcvd: ",DEC AdjRcvd,", Cmd: ",CmdVal, ", Adj: ",DEC AdjVal,13,10]
    ENDIF
    IF LATE THEN                          ' if command took too long
        HIGH LATE_LED                      '  Turn ON LATE LED
        LATE = 0                          '  reset the LATE flag
        LATEtime = LEDonDELAY              '  start countdown till LED-OFF
        HSEROUT ["Late",13,10]
    ENDIF
GOTO Main

'*********** Process received command **************************************
ProcessCmdAdj:
'    varResult = myArray[0]*100 + myArray[1]*10 + myArray[2]

    HSEROUT ["Cmd: ", CmdVal, _  ' send Command, Length of Adjustment & Adjustment value and CR/LF
        ", LenAdj: ", LenAdjVal, " [", DEC LenAdjVal, "]", _
          ", Adj: ", myArray[0], myArray[1], myArray[2], 13, 10]
       
       
        '  ", Adj: ", AdjVal, " [", DEC AdjVal,"]", 13, 10]

    state      = 0              ' indicate CMD & ADJ has been processed

    cmdVal    = 0
    LenAdjVal  = 0
    AdjVal    = 0

    For i = 0 to (ArrayLength - 1) ' clear out array
        myArray[i] = 0
    NEXT i

RETURN

' ***************************************************************
' [TMR1_INT - interrupt handler]
' ***************************************************************
T1handler:
    IF ERRORtime > 0 THEN                  ' if the Error LED is ON
        ERRORtime = ERRORtime - 1          '  decrement the count
        IF ERRORtime = 0 THEN              '  when it reaches 0
            LOW ERROR_LED                  '  turn the Error LED OFF
        ENDIF
    ENDIF       
    IF LATEtime > 0 THEN                  ' if the LATE LED is ON
        LATEtime = LATEtime - 1            '  decrement the count
        IF LATEtime = 0 THEN              '  when it reaches 0
            LOW LATE_LED                  '  turn the LATE LED OFF
        ENDIF
    ENDIF
    HEARTtime = HEARTtime + 1              ' Toggle heartbeat ~.5sec
    IF HEARTtime = 7 THEN
        HEARTtime = 0
        TOGGLE HEART_LED
    ENDIF     
@ INT_RETURN

' ***************************************************************
' [RX_INT - interrupt handler]
' ***************************************************************
GetBytes:
' TODO: Update code to handle AdjVal > 1 character (an array?)

    HSERIN [Serialdata]                    ' Get the serial data (guaranteed here to have at

    IF Serialdata = SyncByte THEN         
        IF SyncRcvd THEN                  ' if it's a Sync byte,
            state = 0                      '  last command was corrupted; reset 'state'
            ERROR = 1                      '  and indicate error
        ENDIF
        SyncRcvd = 1                      '  indicate Sync was rcvd
    ELSE
        IF SyncRcvd THEN
            IF !ForMe THEN                ' if we haven't rcvd the ID
                IF Serialdata = ThisChipID THEN 'and this byte matches the ID
                    ForMe = 1              '    indicate ID rcvd
                ELSE
                    state = 0              '    Not meant for this chip, reset and wait for next msg
                ENDIF                     
            ELSEIF !CmdRcvd THEN
                CmdVal = SerialData
                CmdRcvd = 1
            ELSEIF !LenAdjRcvd THEN
                LenAdjVal = SerialData               
                LenAdjRcvd = 1
                i = 0
            ELSEIF !AdjRcvd THEN
                AdjVal = SerialData
                myArray[i] = AdjVal
                i = i + 1
                If i = ArrayLength THEN
                    AdjRcvd = 1
                ENDIF
            ELSEIF !MsgRcvd THEN
                If SerialData = TxEndChar THEN
                    MsgRcvd = 1
                ENDIF
            ENDIF
        ENDIF
    ENDIF

@ INT_RETURN

;---[TMR1 reload - interrupt handler]-----------------------------------------
ASM                              ; Calculate Timer Reload Constant
ReloadInst  = 8                  ; # of Intructions used to reload timer
  if ((Prescaler == 1)||(Prescaler == 2)||(Prescaler == 4)||(Prescaler == 8))
MaxCount    = 65536 + (ReloadInst / Prescaler)
TimerReload = MaxCount - (OSC*1000000/4/Prescaler/Freq)
    if ((TimerReload < 0) || (TimerReload > (65535-ReloadInst)))
        error Invalid Timer Values - check "OSC", "Freq" and "Prescaler"
    endif
  else
      error Invalid Prescaler
  endif
ENDASM

@Timer1 = TMR1L                  ; map timer registers to a word variable
Timer1      VAR WORD EXT
TimerReload  CON EXT              ; Get the External Constant
TMR1ON      VAR T1CON.0          ; Alias the Timers ON/OFF bit

;---Reload Timer1------
ASM
ReloadTMR1
    MOVE?CT  0, T1CON, TMR1ON    ;  1    stop timer
    MOVLW    LOW(TimerReload)    ;  1    Add TimerReload to the
    ADDWF    TMR1L,F              ;  1    value in Timer1
    BTFSC    STATUS,C            ;  1/2
    INCF    TMR1H,F              ;  1
    MOVLW    HIGH(TimerReload)    ;  1
    ADDWF    TMR1H,F              ;  1
    MOVE?CT  1, T1CON, TMR1ON    ;  1    start timer
  INT_RETURN
ENDASM

;---Start/Stop controls -----
StartTimer:
    Timer1  = TimerReload        ; Load Timer
    TMR1ON = 1                    ; start timer
RETURN

StopTimer:
    TMR1ON = 0                    ; stop timer
RETURN

---

Hi,

I think it's "the usual" case of not treating the data the same way in both ends.

It looks to me like you are sending ASCII but you're treating the received data as binary/raw numbers.
If you send the decimal digit '1', store that in myArray[0] and later multiply that by 100 what you'll get is 4900 because 49 is the ASCII code for '1'.
To do what you want you can use ARRAYREAD with the DEC modifier or simply use the aproach you already have but "offset" the values to account for the ASCII encoding.

Code:

---

varResult = ((myArray[0]-48)*100) + ((myArray[1]-48)*10) + (myArray[2]-48)

---

Or you could subtract 48 when receiving the digits.

/Henrik.

Quote:

---

Originally Posted by HenrikOlsson

Hi,

I think it's "the usual" case of not treating the data the same way in both ends.

It looks to me like you are sending ASCII but you're treating the received data as binary/raw numbers.
If you send the decimal digit '1', store that in myArray[0] and later multiply that by 100 what you'll get is 4900 because 49 is the ASCII code for '1'.
To do what you want you can use ARRAYREAD with the DEC modifier or simply use the aproach you already have but "offset" the values to account for the ASCII encoding.

Code:

---

varResult = ((myArray[0]-48)*100) + ((myArray[1]-48)*10) + (myArray[2]-48)

---

Or you could subtract 48 when receiving the digits.

/Henrik.

---

Thanks Henrik! I'll give it a go tonight after work.

Preferably, I'd just send the output of the 8-bit ADC module on the Master chip directly to the Slave (so, 0-255) rather than converting it to ASCII in a 3-digit format (e.g. "027"), but then I can't figure out how to process that in the ISR if I'm only getting one character at a time.

So why don't you? ;-)

Master:

Code:

---

ADResult VAR BYTE
....
....
HSEROUT [ADResult]  '1 byte

---

Slave:

Code:

---

Duty VAR WORD
HSERIN [Duty]  '1 byte

---

But now, if you're trying to debug this by sending te value of Duty to the PC terminal you need to use the DEC modifier so it converts the value to ASCII for display to us humans, HSEROUT [DEC Duty]

/Henrik.

Quote:

---

Originally Posted by HenrikOlsson

So why don't you? ;-)

Master:

Code:

---

ADResult VAR BYTE
....
....
HSEROUT [ADResult]  '1 byte

---

Slave:

Code:

---

Duty VAR WORD
HSERIN [Duty]  '1 byte

---

But now, if you're trying to debug this by sending te value of Duty to the PC terminal you need to use the DEC modifier so it converts the value to ASCII for display to us humans, HSEROUT [DEC Duty]

/Henrik.

---

Thanks again, Henrik. Can I still incorporate this into my ISR? For that to work, the interrupt on Rc would need to fire when 1 byte gets into the buffet, right? So, instead of an array for 3 'characters' (which on their own are 1 byte, right?) I can just grab the next byte after receiving the AdjCmdVal.

Hi,
The UART RX interrupt always* fires for each byte that comes into the RX buffer, there's no way to set a "threshold" on when the interrupt fires. After all, the buffer is only two bytes deep. But yes, you could set your code up so that after proper sync, adress, command etc you grab one byte and that's it.

* Well not always but that's details details details.....

/Henrik.

Quote:

---

Originally Posted by HenrikOlsson

Hi,
The UART RX interrupt always* fires for each byte that comes into the RX buffer, there's no way to set a "threshold" on when the interrupt fires. After all, the buffer is only two bytes deep. But yes, you could set your code up so that after proper sync, adress, command etc you grab one byte and that's it.

* Well not always but that's details details details.....

/Henrik.

---

Thanks again, Henrik. Much appreciated. I'm going to try all this out tonight.

Code:

---

serialbuffer byte [4]
serialbyte var byte
index var byte

…

‘ ooh looky here… a serial byte arrived
for index = 1 to 3
serialbuffer[index] = serialbuffer[index-1]
next index
serialbuffer[0] = serialbyte

---

Now instead of checking for the first byte in the serial string,
check for what you call the termination byte.
I don’t know what that is, so now it’s $FE.

Code:

---


if serialbuffer[0] = $FE then
‘ we know the bytes serialbuffer [0,1,2,3] are the desired 4 byte string in reverse
‘ unless only a partial command was received
if serialbuffer[3] = “S” then
‘ we know now that the entire four byte command was received if there was no serial error
endif
endif

---

Now if you only wanted to grab say byte 2 (beginning counting from zero).

Code:

---


counter var byte
counter = 0

'oh looky here.. a serial byte arrived

if serialbyte = “S” then
counter = 0
else
counter = counter + 1
endif

if counter = 2 then
byteyoucareabout = serialbyte
endif

---

A lot of this will fall apart if another byte of the command can be the same value as the “S” or the termination character,
which is why it’s better to go something close to the first way, and check both start and end chars if they are always the same.