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art
Joined: 21 May 2015
Posts: 181
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| PIC18F452 , 3.3Volt , EX_SISR.C, ESP8266 |
 Posted: Mon Jul 02, 2018 2:52 am |
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Hai,
I've modified EX_SISR.C for communicating PIC18F452 with ESP8266 wifi module. Since this PIC can function with supply voltage 3.3V same as ESP8266, i've connect directly PIC TX pin to RX pin of ESP8266 and PIC RX pin to TX pin of ESP8266.
When PIC send "AT", wifi module will reply "OK", but the problem is the pic will wrongly display the buffer data. What is wrong with my code ? Please help me.
| Code: |
#include <18F452.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=115200, xmit=PIN_C6, rcv=PIN_C7)
#define BUFFER_SIZE 32
BYTE buffer[BUFFER_SIZE];
BYTE next_in = 0;
BYTE next_out = 0;
#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 !!
}
#define bkbhit (next_in!=next_out)
BYTE bgetc() {
BYTE c;
while(!bkbhit) ;
c=buffer[next_out];
next_out=(next_out+1) % BUFFER_SIZE;
return(c);
}
void main() {
delay_ms(5000);
enable_interrupts(int_rda);
#if defined(__PCD__)
enable_interrupts(intr_global);
#else
enable_interrupts(global);
#endif
printf("AT\r\n");
do {
delay_ms(500);
while(bkbhit)
putc( bgetc() );
} while (TRUE);
}
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Ttelmah
Joined: 11 Mar 2010
Posts: 19516
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| Posted: Mon Jul 02, 2018 3:10 am |
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Your PIC can not operate at 3.3v. Minimum supply voltage for the F452, is 4.2v. You need the 18LF452 to operate at 3.3v.
Your PIC is probably 'just working' but with parts not operating correctly....
Also add 'ERRORS' to your RS232 declaration. This is _required_ when using hardware RS232, unless you are adding your own error code. Without this the UART will become hung if more than 32 bytes arrive in your delay. |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Jul 02, 2018 4:25 am |
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Hai Ttelmah,
I've checked the parts datasheet and it say that the operating voltage range (2.0V to 5.5V). I also test EX_SISR.C with 3.3v supply using this PIC18F452, and no problem. Why need signal 4.2v ? |
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temtronic
Joined: 01 Jul 2010
Posts: 9228
Location: Greensville,Ontario
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| Posted: Mon Jul 02, 2018 4:56 am |
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Mr. T is correct, I just checked the datysheet to confirm, that PIC has a MINIMUM of 4.2 volts for VDD. Please check chapter 22, Electrical Specs, see figure 22-1, it graphically shows the allowable operating VDD vs clock speed.
While your part may be operating now, it probably will fail doing some operations or using some other internal peripherals.
This is similar to 'overclocking' a PC motherboard. Sometimes you can get them to go faster but but they aren't designed to do so, and randomly fail.
also....
unless you have 2 compilers, get rid of the IF... in the ISR. Visually it cleans up your code, so you can concentrate on 'real' code making it easier to see possible typos or other errors. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19516
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| Posted: Mon Jul 02, 2018 7:16 am |
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You need to check the version. The datasheet is for both the F, and the LF parts. The range you are quoting is not for your F part.
Electrical Characteristics Figure 22-1, gives the voltage range for the F part.
The table below 22-2, gives the range for the LF part.
In the parameter table. D001, you have one line for the LF part and one for the F part. The line for the F part gives 4.2v minimum, 5.5v max.
Also look at this thread:
<http://www.ccsinfo.com/forum/viewtopic.php?t=57204>
It actually turned out here that the chip wasn't running at the voltage the poster thought, but what is interesting is that the first part that went wrong, was the UART....
| art wrote: | Hai Ttelmah,
I've checked the parts datasheet and it say that the operating voltage range (2.0V to 5.5V). I also test EX_SISR.C with 3.3v supply using this PIC18F452, and no problem. Why need signal 4.2v ? |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Jul 02, 2018 9:00 pm |
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Hi Ttelmah, temtronic,
Thank you very much for your help, I add ERRORS to rs232 declaration and it works !!!
It seems that this PIC18F452 with "F" works fine with supply 3.3V, not as mention in the datasheet. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19516
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| Posted: Mon Jul 02, 2018 11:07 pm |
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It is common for devices to work under their rated voltage. However you may well find it'll fail if the weather gets hot for example. Don't rely on it!.
Yes the UART being hung was the obvious fault in the code.
Glad it worked. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19516
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| Posted: Mon Jul 02, 2018 11:07 pm |
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It is common for devices to work under their rated voltage. However you may well find it'll fail if the weather gets hot for example. Don't rely on it!.
Yes the UART being hung was the obvious fault in the code.
Glad it worked. |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Fri Jul 13, 2018 11:00 pm |
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Dear Ttlemah,
You were right.... once I expand the code, sometimes it is ok and sometimes not ok( no communication)....so finally I've change the PIC to PIC18LF452. |
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