usart echo

[kikirojas]

Hello:
I need to implement an echo rs232 with the 16f628
I have the next code and it only works when I write from keyboard .When I write with my hands "123456789abcdef" from the hyperterminal in my monitor I see "123456789abcdef" it´s ok.
When I like send an text file ( containing "123456789abcdef" )from hyperterminal in my monitor I see "13579bdf" )
The hyperterminal is setting ok ( 1200 bauds , 8 bits ...).
Why in the first way its works ok ? and why in the second way its eats characters ?

#if defined(__PCM__)
#include <16F628A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=1200, xmit=PIN_A0, rcv=PIN_A1,stream=PC)
#endif
#include <stdlib.h>
int c;

void main()
{
printf("Press any key to begin\n\r");

while(TRUE) {

c=fgetc(PC);
fputc(c,PC);

}

}

[treitmey]

When you type it in, there is time in between characters.
When you send it with hyperterm It is really fast and you lose characters.

Try using hardware usart and interupts and buffers.

[Ttelmah]

You need to use the chip's hardware UART (on pins B1, and B2). The problem you have, is you are performing the recieve and transmit in _software_. As such, while the chip is sending, it can't receive. When you type the characters by hand, you are slow enough, that the chip can send the character back in the 'gap' between the typed characters. When you send a file, there is no gap, so while the first character is being sent back, the second character is missed, and so on.

Best Wishes

[kikirojas]

Thank you .
I need the hardware usart for other application. I need the software usart for connect with a gps and its also eat characters .

[John P]

I've done this, but I tell you, it's not for the faint-hearted. You have to write the code for the software UART yourself, because (I'm pretty sure) the CCS code will hog the processor's attention for the full duration of an incoming or outgoing character. You can do better than that if you use an interrupt when the start bit of a character arrives, and then a timer for each data bit. The trouble is, if you're simultaneously sending a character out and receiving one, you've got competing timer demands. So a lot depends on how many characters you have to receive in a burst--would it be acceptable to swallow them and then regurgitate them a little later, and can you guarantee that there won't be more stuff arrriving while you do it? Could you abandon an outgoing transmission and re-start it, if characters start to arrive? Or could the software UART run really, really slowly, so slowly that you could deal with incoming and outgoing bits at different times, so any inaccuracies in timing would be comparatively small?

If you want operation without any restrictions, I think you need 2 processors, or a processor with 2 UARTs. These chips can do a lot, but some things are just asking too much.

[Ttelmah]

Or (of course), why not cheat?.
If you just need to echo the incoming characters, connect the incoming data, to one input of a logic 'and' gate, with the other input from your PIC's transmit pin. Connect the output of the gate to the MAX232 or equivalent handling the transmit. Then when characters arrive, they will be echoed by the _hardware_to the transmit output, and if you send (provided you verify nothing is coming at the time), it too will be sent.

Best Wishes

[SET]