I don't think you are sending a full start bit. (I haven't worked
with any 8051 in a long time, so I'm not even looking at the
hardware specifics.)
This is my crack at rewriting the ISR. Instead of using 'rotate'
to rotate the st_char an increasing number of bits each time, just
keep a partially rotated copy in new variable 'st_temp'.
Also, you only need the 16x interrupt rate for receiving. If you
can cut the rate by 16 on transmit, you could delete 'st_count'
and associated code.
void timer1_isr() interrupt 3
{
if (--st_count) // time to change the bit?
return;
st_count = ST_SPEED;
if (st_status == 0) // send start bit
{
TxD1 = 0;
st_temp = st_char;
}
else if (st_status < 9) // send data bit
{
B = st_temp;
TxD1 = b_0;
st_temp >>= 1;
}
else if (st_status == 9) // send stop bit
TxD1 = 1;
else // done
{
st_status = 0;
return;
}
st_status++;
}
-Ken Jackson
Ulhas Vaidya writes:
> hi,
>
> I am trying to implement a second UART on 89C52 by looking at atmel
> application note no. ANM 055.
> On a simulator I see the P3.4 (corresponding to TxD) changing properly but
> nothing gets received by a computer. The connections are fine. I am
> appending the code below wherein character 'A' is intended to be transmitted
> continuously.. I shall be thankful for any help / insight.
>
> #define TxD1 P3_4
> #define RxD1 P3_3
>
> #define ST_SPEED 16
>
> bit sr_ready;
> bit sr_error;
> bit sr_incom;
>
> unsigned char sr_ch;
> unsigned char sr_count;
> unsigned char sr_status;
> unsigned char sr_char;
> unsigned char rotate;
> unsigned char st_char;
> unsigned char st_count;
> unsigned char st_status;
>
>
>
> void timer1_isr() interrupt 3
> { unsigned char a;
>
> if(!st_status) {TxD1=1; TxD1=0; st_count= ST_SPEED; st_status++; return;}
> //send start bit
> st_count--; if(st_count!=0) { return;} // time to change the bit?
>
> if(st_status<=8) { a=st_char>>rotate; B=a;TxD1=b_0; st_count=ST_SPEED;
> rotate++;st_status++; return;} //send bit
> else if (st_status==9){ st_ready=1; TxD1=1; rotate=0; st_count=
> ST_SPEED;st_status++;return;} // send stop bit
> else if(st_status>9) { st_status=0;return;}
> }
>
>
> void main()
> { rotate=0;
> st_char ='A'; st_count=ST_SPEED; st_status=0; TCON=0x40; TMOD=0x20;
> TH1=0xe8; SCON=0x52;
> PCON=0; ET1=1; EA=1;
> while(1){}
> }
>
> --
> Ulhas Vaidya
> Cell No: 098695 74699
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