Can't get TI flag to be set when writing into SBUF

hi,

When I write into SBUF, the TI flag doesn't
go high

Is UART configured right? Have you initialized and run clock source for UART (timer, BRD...)?

Regards,
Oleg

hi,

When I write into SBUF, the TI flag doesn't
go high

Is UART configured right? Have you initialized and run clock source for UART (timer, BRD...)?

Regards,
Oleg

Initialization Seems OK to me.
The Initialization code as given below.

SCON = 0x50;
/* mode 1: 8-bit UART, enable */
TMOD = TMOD | 0x20;
/* timer 1 mode 2, 00100000b */
TH1 = 0x87;
/* 600 BAUD @ 20 MHZ */
TR1 = 1;
/* timer 1 ON */
TI = 1;
/* Set TI to send first char */
ES = 1;
/* enable serial port interrupt */
EA = 1;
/* enable interrupts */

a)When I write into SBUF, the TI flag doesn't
go high even though I have enabled interrupts.

b)TI = 1;
/* Set TI to send first char */
a) TI should set regardless of interrupts enabled or not.
b) probably not a problem, but I would set TI after the interrupt is enabled.

anyhow, the first thing your ISR should do is to clear TI, could it be that it does get set, but you do not catch the state before it is reset in the ISR?

Try a breakpoint between set TI and int enb.

Erik

Erik

hi eric,
that's not an issue as I'm stepping through
my program using the debugger.

The problem is I'm not able to SIMULATE the
TI flag going high.

For example if I want to simulate the RI flag
first I run the initialization routine
[as shown above].
then I write into the command line (or debug scrip) SIN = 0x43 (or any other value)
and you will see that the RI flag going high
in the peripherals/serial window,
and suppose you have

void serial() interrupt 4
{
if (RI == 1)
{
keypressed = SBUF; RI = 0;
}

Then I can actually see that 0x43 is being
written to keypressed before RI being cleared.

But I can't see the TI flag raise when I try reading SOUT or writing to SBUF.

hi,

assume you have wrote something like that:

void serial() interrupt 4
{
//... receive code
//...
if (TI == 1)
{
   TI = 0;
   SBUF=0x34;
}

Baud Rate calculator:

http://www.keil.com/c51/baudrate.asp

Hey Guys,

That was not the problem. It can work
at any Baud rate. Finally got it
working by seeing the HELLO.c in Examples,
but I don't know how!.

Here is my code:-
if (TI == 1) /* check for transmit interrupt flag */
{
TI = 0;
P1 ^= 0x01; /* Toggle P1.0 each time we print */
SBUF = "H";
}

Also Need to keep the serial window open for
the output to print.

Still can't understand why TI flag doesn't
raise if I don't toggle port pin 1.0 (T2).

Thanks.

Perhaps you could post the smallest complete, compilable program which shows the problem.

Please cut and paste this from your editor to guarantee that what you post is what you are using.

Hi VK,
I am have facing the same problem as you have mentioned i.e not able to get TI interrupt but for some reason but RI interrupt is immediately addressed when I press a key.
I was under the impression that as soon as you write something to SBUF you would get TI interrupt but it does not happen. Do you have any additional information on this?
Please reply to my hotmail id (rohitsivakumar@hotmail.com)

TI is set after the entire Byte plus the start and stoip bit are transmitted. That is the point of doing it with an interupt.you can do other things while waiting for the byte to finish leaving. If it set immediatly why would you need to look at it. Set a break point at you serial interupt. It will get there. It may take awhile single stepping.