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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Thu Feb 16, 2006 2:14 pm |
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| Quote: |
kbhit() wait for the start bit of an incoming character.
Is the only way to wait for a start bit using software UART
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The fgetc() function does wait for the start bit with a soft UART.
In the test program below, I have forced the compiler to create
a software UART on pins C6 and C7. It waits for each keypress.
If I press abcde, etc., it displays:
I tested this with PCM vs. 3.242.
| Code: |
#include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, FORCE_SW)
void main()
{
char c;
while(1)
{
c = fgetc();
printf("%c", c);
}
} |
Here is the first part of the .LST file. It shows the code for a soft UART.
I have added comments to show what the code is doing. It waits in
a loop until a start bit is found. This shows that fgetc() does wait for
the start bit.
| Code: |
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, FORCE_SW)
0004 3008 MOVLW 08 // 8 bits per character
0005 00F7 MOVWF 77
0006 17A0 BSF 20.7 // Set TRISC.7 in shadow register
0007 0820 MOVF 20,W
0008 1683 BSF 03.5
0009 0087 MOVWF 07 // Move shadow reg. to TRISC
000A 1283 BCF 03.5
000B 1F87 BTFSS 07.7 // Test if rcv pin = 1 (idle state)
000C 280F GOTO 00F // If rcv = 0, jump (start bit)
000D 1683 BSF 03.5
000E 280A GOTO 00A // Stay in loop if rcv pin = 1
// Jump here if start bit is found.
000F 01A2 CLRF 22
0010 17F7 BSF 77.7 // Set flag to indicate start bit
0011 2820 GOTO 020
0012 13F7 BCF 77.7
0013 2820 GOTO 020
0014 1003 BCF 03.0
0015 1B87 BTFSC 07.7
0016 1403 BSF 03.0
0017 0CA2 RRF 22,F |
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Ttelmah
Guest
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| Posted: Thu Feb 16, 2006 3:04 pm |
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The obvious question is how is the serial connected.
Basically kbhit, will advance when it sees the incoming signal as low. Now you say you have tested it as 'high', but how soon after the board is powered is this?. It is possible, that all that is wrong, is that the line does not reliably go high, till some time after the board is powered, and the code is getting through it's tests before this happens.
Best Wishes |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Fri Feb 17, 2006 2:50 am |
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| Quote: | | #use delay(clock=48000000) |
48MHz ....... 
There is no PIC processor available at this moment that will run that fast! Your RS-232 timing is totally screwed up.
Also, when I asked for your compiler version I'm not only interested to know if it is PCW, PCH or any other compiler flavour, but I want to know the version number as well (v3.xxx). You can find this version number at the top of the *.lst file and in some other places. |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Fri Feb 17, 2006 4:44 am |
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| Quote: |
kbhit() wait for the start bit of an incoming character.
Is the only way to wait for a start bit using software UART
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What I wrote is right. kbhit() wait for the start bit of an incoming character.
| Code: |
................... do{
.................... }while(!kbhit(commu));
0057: BTFSC PORTA.2
0058: GOTO 057
.................... |
The big difference is that kbhit() test for the start bit and if it is not true, skip to do another short task.
Instead fgetc() sit and wait in a loop until it receive a character. While it is into the waiting loop,
can't do another task.
ckielstra wrote: | Quote: |
There is no PIC processor available at this moment that will run that fast! Your RS-232 timing is totally screwed up.
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I guessed this when I asked him if he did a software delay test.
Humberto |
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Ttelmah
Guest
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| Posted: Fri Feb 17, 2006 6:23 am |
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As it stands, XTPLL, and PLL1, means there will be 4MHz going into the USB prescaler. This will then give 96MHz from the USB PLL, which is the divided by two, to feed the USB circuitry with 48MHz.
The 96MHz, is then fed to the CPU divider.
CPUDIV, is not specified, so will be /2
The clock frequency to the processor, will then be 48MHz, _which this processor does support_. Provided the supply voltage is 4.2v or higher, this processor is rated to run at 48MHz. It is one of only a very few PICs that can do this.
So the question is, what voltage the chip is running at. If it is below 4.2v, then the selected frequency won't work. The fact that 'BORV', was set at 2v (but commented out), suggests the voltage may be lower.
As a comment, there is an erratum, relating to BORV, and if the bits for this register are set to '11', the chip may not function. This may well be the default, so putting a value in, or checking what the value is set to, may be worthwhile.
Best Wishes |
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ADN
Joined: 23 Dec 2005
Posts: 9
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| Posted: Fri Feb 17, 2006 1:54 pm |
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@ckielstra: the compiler version is 3.236
@Humberto: I have already used fgetc() without kbhit() but it didnt wait for any characters and it has always 0x00 character received without that I have sent any characters!
Apprarently there is a problem with the UART functions of the compiler but I dont know how to write new ones
@Ttelmah:
It is exactly like you have explained.
I am using a 3,3 V supply voltage and all other parts of my circuit (including an other RS232, I�C, SPI and USB) are running smoothly.
| Quote: |
As a comment, there is an erratum, relating to BORV, and if the bits for this register are set to '11', the chip may not function. This may well be the default, so putting a value in, or checking what the value is set to, may be worthwhile.
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I didnt get the point here. could you explain this please!
ADN |
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Ttelmah
Guest
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| Posted: Fri Feb 17, 2006 3:39 pm |
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If you are using 3.3v, then you need to specify the CPUDIV value, and bring the clock down to 20MHz. The chip is only specified to run to 20MHz max at 3.3v...
I suspect that at the lower voltage, the chip is probably locking onto an undertone, and is running at perhaps 32MHz, or 24MHz, which will make the serial timings fail.
The 'point' is that there is an erratum on the chip that can stop it working on the current silicon versions, if the BORV bits are set to '11'. Hence you should be specifying a reset voltage, and make sure that the value specified is one that does not give this bit combination. This bit combination, corresponds to the 2v setting, and may well be the default, so select the next voltage setting 'up', and program this in the settings.
Best Wishes |
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