Problem with 9-bit Addressing

[andyfraser]

Hi,

I am trying to use 9-bit addressing on my RS485 link using a PIC16F877. I cannot get the receive interrupt service routine to be called when set to interrupt on an address but do when I set it to interrupt on data. An extract of the code I am using follows.
As you can see from the code, I set PIN_B5 low then high in the receive ISR. With the initialisation code shown below, I get no activity on B5 however, if I change the line setup_uart( UART_ADDRESS ) to setup_uart( UART_DATA ), I see a pulse for each character on the bus !
Any help would be much appreciated.

Andy

At top of program:

#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7,enable=RS485_ENABLE,bits=9,long_data,errors,stream=RS485 )

Initialising:

setup_uart( UART_ADDRESS );
setup_uart( TRUE );
output_low( RS485_ENABLE );

//
// Turn on the serial interrupts
//
enable_interrupts( INT_RDA );
enable_interrupts( GLOBAL );

Sending:

int8 i;
int8 cs = 0;

//
// Send address
//
fputc( (int16)0x100 | g_Packet[ 0 ],RS485 );

//
// Send the remaining data with the 9th bit clear
//
for( i = 1 ; i < PACKET_LEN ; i++ )
{
cs += g_Packet[ i ];
fputc( g_Packet[ i ],RS485 );
}

//
// Now send the checksum
//
fputc( cs,RS485 );

Receiving:

#int_rda
void rx_isr()
{
int16 b;

output_low( PIN_B5 );

//
// Get received charcater
//
b = fgetc( RS485 );

output_high( PIN_B5 );
}

[Ttelmah]

[andyfraser]

Ttelmah,

Thanks for the reply but if you look in the body of the code you will see that I don't use putc and getc, i use fputc and fgetc. According to the example code for multi-drop programming (rs485.c) I can send a 16-bit value through fputc. I think this is a feature added recently to the compiler, so I should have explained that I am using version 3.184. Out of interest, I got the code working by manipulating the UART bits directly as shown below.

[Ttelmah]

[andyfraser]

Ttelmah,

To quote the readme.txt file that came with my version of the compiler :


New options for #UASE RS232:
SAMPLE_EARLY
A getc() normally samples data in the middle of a bit time. This option causes the sample to be at the start of a bit time. May not be used with the UART.

RETURN=pin
For FLOAT_HIGH and MULTI_MASTER this is the pin used to read the signal back. The default for FLOAT_HIGH is the XMIT pin and for MULTI_MASTER the RCV pin.

MULTI_MASTER
Uses the RETURN pin to determine if another master on the bus is transmitting at the same time. If a collision is detected bit 6 is set in RS232_ERRORS and all future PUTC's are ignored until bit 6 is cleared. The signal is checked at the start and end of a bit time. May not be used with the UART.


LONG_DATA
Makes getc() return an int16 and putc accept an int16. This is for 9 bit data formats.


DISABLE_INTS
Will cause interrupts to be disabled when the routines get or put a character. This prevents character distortion for software implemented I/O and prevents interaction between I/O in interrupt handlers and the main program when using the UART.

See RS485.C in the drivers directory for an example RS485 protocol implementation.


However, I could not get this to work correctly and as mentioned in my previous reply, I had to bash the UART registers directly

Andy

[Ttelmah]