USB to RS232 adapter

[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

[Darrel Taylor]

That was pretty quick!

I've been playing with the program here and can say that the two PAUSE 25 statements, have to GO.

Of course that messes up the LED's, but with the pauses in there, it only picks up every 7 or 8th character when sending continuous data.

Without them, it works pretty good, but it's still a bit slow.
Test data of about 1500 bytes takes nearly 3 times as long as it should. Around 1.2 sec.

I think circular buffers would help speed it up, since it has to wait till it's finished sending the HSEROUT before in can receive more data from the USB. But I guess that depends on how fast you need it to be.

[PJALM]

Thanks Darrel. I have eliminated the LEDs all together because there is really no need for them. I was testing it by just using a terminal program on 2 computers so I never noticed the speed problem till now. How do I impliment the circular buffers you mentioned?

[Darrel Taylor]

Me and my big mouth.

I wish I had time to work something up, but I've got too many things going on already.

You might take a look at this post by Joe S.
http://www.picbasic.co.uk/forum/showthread.php?p=28233

He's got a buffer in there for serial RX. Should give you a start.
But you really need to buffer both RX and TX.

busy busy,

[Squibcakes]

Hi Guys I've been working on the same - I can get a Half duplex data communication going but not full duplex (rs232-> usb and vice versa).

This program seems to do the trick, but even with the pauses removed I still only achieve a stable data rate at 9600 when sending large text files.

I'll try using the DT method (DT_int_18) interrupts and see if this speeds things up.

Circular buffers? The mind boggles!

Cheers

[mister_e]

i doubt it would be if you used the EUSART but may worth to try..

PicMultiCalc gaves me...

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 225 ' 9600 Baud @ 48MHz, 0.0%
SPBRGH = 4
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator

mixing INT_18 and asm would certainly have some great effect.