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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| serial funnies 16f88x vs 16C74x |
 Posted: Tue Dec 22, 2009 4:29 pm |
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I have some 16C74 A & B chips - they BOTH show the same problem.
If you comment out the two 16c74 related lines && compile for the 887 (or even 877) - the code works perfectly and echoes all data arriving perfectly.
At baud rates from 4800 to 76800 - perfection. This was designed to find the fastest safe baud rate for the 74 family - to try to use up a stockpile of a few thousand new (otherwise surplus) 74A's and B's on a cost sensitive product.
BTW: the host uses a crystal controlled TI 16550 UART with dead on clock accuracy and the 887 in the same test fixture can loop back data flawlessly @ 76800 baud without a single error char for 48 hours non stop using this code !!
Yes I know there is an error warning on the c74 family above, 9600 baud but when compiled even at 4800 baud - the greeting is always output - but no receive data is ever echo'd with the C74 -
the LST file is not very illuminating 2 me - and I think I must have missed something obvious - but damned if I can tell. I can't even see WHERE the compiler is setting BRGH or NOT, since it does not seem associated with the setup of USART services !!!
Does anybody have a clue ?
| Code: |
// #include <16f887.h>
// #FUSES NOPROTECT,NOMCLR,HS,NOWDT,NODEBUG,NOLVP,NOIESO,NOFCMEN,PUT,NOWRT,NOFCMEN
#include <16c74a.h>
#Fuses HS,NOWDT,PUT,NOPROTECT,BROWNOUT
#include <stdlib.h>
#use delay( clock=4915200)
#use fast_io(C)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS )
#define BUFFER_SIZE 48
BYTE RISR_out; // global background newchar from ISR BACKGND buffer
BYTE buffer[BUFFER_SIZE];
BYTE next_in = 0;
BYTE next_out = 0;
// interrupt receiver code
#define bkbhit (next_in!=next_out)
// I ONLY call if bkbhit is true
void bgetc(void) {
RISR_out=buffer[next_out];
next_out=(next_out+1) % BUFFER_SIZE;
}
void DISR_INIT(void){
clear_interrupt( int_rda );
enable_interrupts(int_rda);
enable_interrupts(global);
}
#int_rda
void serial_isr() {
int t;
buffer[next_in]=getc();
t=next_in;
next_in=(next_in+1) % BUFFER_SIZE;
if(next_in==next_out) next_in=t; // Buffer full !!
}
//***********************************
void InitHDW ( void ) {
//***********************************
set_tris_c (128); // set bit 7 per datasheet for C7=INPUT
DISR_INIT();
}
//===================================
void main() {
InitHDW(); printf ("*Hello*\r"); // just check output
while (1) { // now get AND send at same time
if (bkbhit) { bgetc(); putc(RISR_out);} //simple test
} // END : while 1
}
//
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Tue Dec 22, 2009 9:26 pm |
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ver 4.066 --
did not try 8 MHz - and may not now -
I used the 4.9152mhz ( plug in 14 pin OSC can - have 10K in inventory )
because it gives perfect divisors with BRGH=0 up to 76800
I thought based on the baud rate that staying with a zero error baud
master freq was desirable - now I'm tempted to use a software RX channel instead on the B port INT pin.
BTW - I had the exact SAME problem of NO work at all with the 16c65A - which I have quite a few of ( too many I think ) too - and it sucks just as bad.
Because this is a new limited production design - I have total flex with the circuit design and software - & my boss would LOVE 2 use up these parts - AND its being serial/ USB translated with an FTDI UM232R - plus baud rate not critical - I can go down to 2400 baud and still be fine..
The TX side hardware is A-ok.
I had HOPED there was some software glitch - because finding SOME bad chars was one thing -but NO hardware RX at ALL - really sucks!
Thanks PCM 4 the concise link to the bad new s;-)) |
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