USB to RS232 adapter

[Darrel Taylor]

Or, if you wanted to stick with PicBasic, you could try the usbcdc.bas example in the USB18 folder.

[PJALM]

I have looked at booth but they are incomplete.

I have tried to capture data from the RS232 port on the pic and output it to the USB and also from the USB to the RS232 with no sucess.

All examples are just on how to emulate the CDC.

I basically need a USB to RS232 adapter like those you can buy in any store.

I have tons of these 18F2550 chips and would rather use them to convert my exsisting projects instead of going and buying some.

[PJALM]

Ok, I got it to go from USB to the RS232 but I still cannot get the RS232 to USB to work. Here is the code I have so far.

DEFINE  OSC 48

INCLUDE "modedefs.bas"

Buffer   VAR BYTE[16]
Cnt      VAR BYTE
B0       VAR BYTE

PIC_TX   VAR PORTC.6     ' Transmit Pin
PIC_RX   VAR PORTC.7     ' Receive Pin

ADCON1 = 15              ' Set all I/Os to Digital
INTCON2.7 = 1            ' Disable PortB Pullups         
CMCON = 7                ' Disable Comparators

USBInit

' Main Program Loop
MainLoop:
    USBService           ' Must service USB regularly
    cnt = 16
    USBIn 3, Buffer, Cnt, MainLoop

    SEROUT2 PIC_TX,84,[STR Buffer\Cnt]
    
Get_RS232_Data:
    SERIN PIC_RX,T9600,100,Get_RS232_Data_Timeout,B0
    Buffer[0] = B0
    Cnt = 1
    GOTO OutLoop
    	
Get_RS232_Data_Timeout:
    Buffer[0] = 0
    Cnt = 0
    
OutLoop:
    USBService          ' Must service USB regularly
	
    IF Cnt > 0 Then
        USBOut 3, Buffer, Cnt, OutLoop
    ENDIF

    GOTO Mainloop

[skimask]

Using a MAX232 type chip in the circuit?
Depending, you might have to use N9600 instead of T9600

[PJALM]

Yes, I am using the MAX232 between the PIC18F2550 and the RS232 port.

[Darrel Taylor]

At a quick glace, there's a couple problems. Maybe more, but haven't tested it yet.

With the first USBIN, if there isn't any incoming data from USB, it just loops back to MainLoop. It never makes it to SERIN, unless it receives data from USB at the same time.

You really should use HSERIN. The RS232 data may start while the program is sending or receiving USB data, in which case you would not be able to catch it with SERIN.

Added: And the 100ms timeout on the SERIN will cause it to lose the USB connection, since it isn't servicing it anymore.

[PJALM]

Ok, I got it all working now. I took Darrel's advice and switched to using HSERIN and HSEROUT but added the use of hardware interrupts to capture the RS232 data.

Here's the new code:

DEFINE    OSC 48
DEFINE    HSER_RCSTA   90h
DEFINE    HSER_TXSTA   20h
DEFINE    HSER_BAUD    9600
DEFINE    HSER_CLROERR 1

INCLUDE "modedefs.bas"

Buffer    VAR BYTE[16]
Cnt       VAR BYTE
B0        VAR BYTE
PIC_TX    VAR PORTC.6     ' Transmit Pin
PIC_RX    VAR PORTC.7     ' Receive Pin
LED1A     VAR PORTB.0     ' 2 Color LED #1
LED1B     VAR PORTB.1
LED2A     VAR PORTB.2     ' 2 Color LED #2
LED2B     VAR PORTB.3

ADCON1 = 15               ' Set all I/Os to Digital
INTCON2.7 = 1             ' Disable PortB Pullups         
CMCON = 7                 ' Disable Comparators

'-------------------------------------------------------------------------------
' Interrupt Settings
'-------------------------------------------------------------------------------
RCON.7 = 0                ' Disable Priority Interrupts, 1 to Enable

' Enable/Disable Interrupts
INTCON.4 = 0              ' Disable INT0 (PORTB.0)
INTCON3.3 = 0             ' Disable INT1 (PORTB.1)
INTCON3.4 = 0             ' Disable INT2 (PORTB.2)
INTCON.5 = 0              ' Disable TMR0 (Timmer 0)
INTCON.6 = 1              ' Enable Peripheral Interrupts
INTCON.7 = 1              ' Enable Global Interrupt Handler
PIE1.4 = 0                ' Disable USART Transmit Interrupt
PIE1.5 = 1                ' Enable USART Receive Interrupt
PIE2.5 = 0                ' Disable USB Interrupt

LOW LED1A                 ' Turn LED #1 Green
HIGH LED1B
LOW LED2A                 ' Turn LED #2 Off
LOW LED2B

PAUSE 500

USBInit

ON INTERRUPT GOTO Main_Interrupt_Handler
ENABLE INTERRUPT

' Main Program Loop
MainLoop:
    USBService            ' Must service USB regularly
    Cnt = 16
    USBIn 3, Buffer, Cnt, MainLoop

    HIGH LED2A
    PAUSE 25

    HSEROUT [STR Buffer\Cnt]

    LOW LED2A
    
    GOTO Mainloop
	
	
'-------------------------------------------------------------------------------
' Interrupt Handler
'-------------------------------------------------------------------------------
    DISABLE INTERRUPT     ' No Interrupts past this point
Main_Interrupt_Handler:

    '---------------------------------------------------------------------------
    ' USART Transmit Interrupt
    '---------------------------------------------------------------------------
    IF PIR1.4 = 1 THEN
        PIR1.4 = 0
    ENDIF
    '---------------------------------------------------------------------------

    
    '---------------------------------------------------------------------------
    ' USART Receive Interrupt
    '---------------------------------------------------------------------------
    IF PIR1.5 = 1 THEN
        HIGH LED2B
        PAUSE 25
        
        HSERIN [B0]
        Buffer[0] = B0
        Cnt = 1
    
OutLoop:
        USBService        ' Must service USB regularly
        USBOut 3, Buffer, Cnt, OutLoop

        LOW LED2B

        PIR1.5 = 0
    ENDIF
    '---------------------------------------------------------------------------

IntDone:
    RESUME                ' Return to main program
    ENABLE INTERRUPT
'-------------------------------------------------------------------------------

    END