should i use max 232 with USB to DB9 connector?

when you connect a db9 cable from your PC which has a db9 serial port then you use max232 ic to interface with you controller. but if i but a usb to db9 connector than do i need max232 pin on my circuit? i dont know but i believe that their is already max232 ic in that connector???

Hi,

It depends on the cable you buy.

Many are USB to Serial RS232 , they quote ' Support RS232 serial interface' - so as you say will have a max232 or similar in there to send/receive the rs232 level signals, so your micro needs a max232 to mate with.

There are a few as USB to Serial TTL which will connect directy to a 5v micro.

Sajjadkhan said:

... but if i but a usb to db9 connector than do i need max232 pin on my circuit? i dont know but i believe that their is already max232 ic in that connector???

Click to expand...

Even if there is a MAX232 inside the DB9 connector, you still need an inverter, and MAX232 provides both: level conversion and signal inversion.
Otherwise, if the USB-RS232 cable can accept 0-5V, you may use single-transistor inverters in both directions with pull-up resistors hocked-up between the uC pins and 5Vdc ..

:wink:
IanP

using hyper terminal when i click the connect icon then voltage on pin 4(Data terminal ready) and pin 7(request to send ) goes to 5v. As i have never used DB9 port do u thing the opposite happens in Db9 com port as far as the polarity is concerned?

and if i do need an inverter transistor then do i need it for evey pin i.e. Rx,Tx,RTS and CTS as i m going to use enhance usart mode. thanks.

Sajjadkhan said:

using hyper terminal when i click the connect icon then voltage on pin 4(Data terminal ready) and pin 7(request to send ) goes to 5v. As i have never used DB9 port do u thing the opposite happens in Db9 com port as far as the polarity is concerned?

and if i do need an inverter transistor then do i need it for evey pin i.e. Rx,Tx,RTS and CTS as i m going to use enhance usart mode. thanks.

Click to expand...

My advice is: loop the hanshake signals (RTS, CTS, ....) and don't worry about them ..
In 99% of cases they are irrelevant ..
See attached picture on how to configure the DB9 connector for the handshake loops .. and 3 usables: Rx, Tx and GND

:wink:
IanP

Thanks for the reply but its not working. i am not using max232 because signal level is not more than 5.1V.
I am using this cable:

**broken link removed**

- - - Updated - - -

i am trying to send a character using example in mikroC help, i just editted it to send just one character over and over .

char uart_rd;

void main() {
ANSELH = 0;
ANSEL = 1;
TRISB = 0;
TRISA = 1;

UART1_Init(9600); // Initialize UART module at 9600 bps
Delay_ms(100); // Wait for UART module to stabilize

while (1) { // Endless loop
//if (UART1_Data_Ready()) // If data is received,
//{
//uart_rd = UART1_Read(); // read the received data,
uart_rd = "H";
UART1_Write(uart_rd); // and send data via UART
//}
}
}

Sajjadkhan said:

Thanks for the reply but its not working. i am not using max232 because signal level is not more than 5.1V

Click to expand...

Even if the levels are around 5V, you still have to invert the signals.
When you connect inverters, loop Tx through Rx and using Hyperterminal test the loop.

:wink:
IanP