Variable passing to sub

[Nobody/Anonymous]

I am writing a bootloader in GCBASIC but found the USART empty so decided to write my own. Here is a sample based on code by Steve on forum.

'USART test routines
#chip 16F877A,10
#option bootloader

#define SPBRG_Val 0x40

Initusart

mainloop:
wait 25 ms
HserTX_Print ("Please type in a character ")
HserTX(13)
HserTX(10)
Loopx:
inbyte = HserRX
If inbyte=0 then GOTO Loopx
HserTX_Print ("Message received, you entered a: ")
HserTX(inbyte)
HserTX(13)
HserTX(10)
goto mainloop

sub initusart
    BSF TRISC,6            'PORTC.6 output
    BSF    TRISC,7            'PORTC.7 output
    MOVLW    SPBRG_Val        'baude rate
    MOVWF    SPBRG
    movlw    0x24        'enable transmission and BRGH=1
    movwf    TXSTA
    movlw    0x90        'enable serial port and receive
    movwf    RCSTA
end sub

sub HserTX (xmitdata)
LoopTransmit:
IF PIR1.TXIF OFF THEN goto LoopTransmit 'check if transmitter is busy
TXDATA = xmitdata
TXREG = TXDATA 'transmit data
end sub

sub HserTX_Print(PrintData$)
PrintLen = PrintData(0)
if PrintLen = 0 then exit sub
for SysPrintTemp = 1 to PrintLen
HserTX(PrintData(SysPrintTemp))
next
end sub

function HserRX 'check if data received, and if so, return data
IF PIR1.RCIF OFF THEN GOTO endreceiveserial
HserRX = RCREG
GOTO successreceiveserial
endreceiveserial:
HserRX = 0 
successreceiveserial:
end function

function HserIn
HserIn = RCREG
end function

This version works; however, if I change SPBRG_Val to a variable

Dim SPBRG_Val as byte

SPBRG_Val=0x40

Now it does not work.

I also tried

sub initusart(baude)#NR
    BSF TRISC,6            'PORTC.6 output
    BSF    TRISC,7            'PORTC.7 output
    MOVLW    baude        'baude rate
    MOVWF    SPBRG
    movlw    0x24        'enable transmission and BRGH=1
    movwf    TXSTA
    movlw    0x90        'enable serial port and receive
    movwf    RCSTA
end sub

and called it with

initusart SPBRG_Val

This did not work. I also changed (baude) to (baude as byte).

Are variables all global or are variables defined in a subroutine, local variables.

[Hugh Considine]

These lines are causing the trouble:

MOVLW SPBRG_Val 'baude rate
MOVWF SPBRG

"movlw" is used to load a literal (fixed number) into W (the accumulator). When using a number like 0x40, this works fine and places the correct value into W for the next instruction (move W into file register (variable) SPBRG. However, when "movlw variable" is used the address of the variable is loaded into W. This means that SPBRG is getting set to the location of SPBRG_Val, not its value.

The solution is to replace this assembly with a line of GCBASIC code:

SPBRG = SPBRG_Value

Another alternative is to change the first line to "movf SPBRG_Val,F", but I'd advise against using assembly code except where necessary.

[Nobody/Anonymous]

That was the problem. Undone by the obvious.