uVision 5 - printf function does not work

I am working with the C8051F580 using a custom board.

I use UART0 to communicate with TERATERM. 115200 bps

currently I am using a simple routine to write to the terminal, see below. this works

void send_byte(unsigned char byte)
{
while(tx_busy); // Wait until tx queue is free
tx_busy = 1; // Set uart tx busy
SBUF0=byte; // Transmit byte
}

But now I need to format text.

is there specific setting needed for the printf function to work

I have tried just sending printf("test \r\n") but I get nothing on the screen.

any suggestions will be appreciated.

Thank you 

Fausto Bartra