How to receive stream of bytes using PIC USART

[mackrackit]

If you do not want to setup all of the defines and want to change things around on the fly here is an example that I use for testing on a particular chip. Displays the serial input on an LCD. The RCSTA.4 part clears any overruns.

Did you have a MAX232 or equivalent when you tried the hardware serial?

'******************************************
'18F6680   02/14/09  INFEED PARSE TEST BAUD 9600
    DEFINE OSC 20
    @ __CONFIG    _CONFIG1H, _OSC_HS_1H
    @ __CONFIG    _CONFIG2H, _WDT_ON_2H & _WDTPS_128_2H
    @ __CONFIG    _CONFIG4L, _LVP_OFF_4L
    DEFINE LCD_DREG     PORTG 
    define LCD_DBIT     0
    DEFINE LCD_RSREG    PORTE 
    DEFINE LCD_RSBIT    0
    DEFINE LCD_EREG     PORTE 
    DEFINE LCD_EBIT     1
    DEFINE LCD_BITS     4 
    DEFINE LCD_LINES    4
    DEFINE LCD_COMMANDUS    3000 
    DEFINE LCD_DATAUS   150
  '###############################################
    PAUSE 100 : LCDOUT $FE,1,"TEST"
    N1 VAR LONG:N2 VAR LONG
    START: N1 = 0 : N2 = 0
    HIGH PORTG.4 :PAUSE 250:LOW PORTG.4
    RCSTA.4 = 0 : RCSTA.4 = 1
    'CHANGE LINE FEED AND CARRIAGE RETURN AS REQUIRED 
    RCSTA=$90:TXSTA=$24:SPBRG=129:HSERIN[WAIT($a),WAIT($d),DEC N1,WAIT(","),DEC N2]  
    LCDOUT $FE,1,DEC N1 : lcdout $FE,$C0,DEC N2 : GOTO START

[Ioannis]

What is the exact data sent from the SpO2 module? Is there any header that can be identified befor getting data?

I mean does the module send out "Hey! Data coming" and then the measurements each time?

If the measurements are sent out continusly without any header, then your PIC is reading at random times, confusing the data frames between them.

You have to find a way to just wait for the start of each frame and then grab the next data.

Ioannis

[unifoxz]

mackrackit: Did you have a MAX232 or equivalent when you tried the hardware serial?

I don't use MAX232 for this circuit. I use a 22k resistor at Rx pin and 1k resistor at Tx pin. May I know is there any effect for not using MAX232? There is another question that I would like to know: can MAX3232 be used to replace MAX232?

Ioannis: What is the exact data sent from the SpO2 module? Is there any header that can be identified befor getting data?

The first byte of the 5 bytes data block starts with the synchronous bit of '1' while the other bytes start with bit '0'. This is the only identifier I could use to detect the the data bytes (SpO2 and pulse rate) I need.

I tried to check the bytes sent from the module since the starting of the module operation. The data might be correct for the first few bytes but the continuous bytes are all wrong.

My problem is similar to retransmitting a big file (in MB) through PIC. The file sent out from the PIC is not the same as the file before it was sent to the PIC. The PIC cannot handle a stream of continuous bytes and thus causing data went wrong.

[mackrackit]

I don't use MAX232 for this circuit. I use a 22k resistor at Rx pin and 1k resistor at Tx pin. May I know is there any effect for not using MAX232? There is another question that I would like to know: can MAX3232 be used to replace MAX232?

Yes, I used a 232. From the PIC Hardware Serial to a PC some kind of level inverter is needed. The PICs sends in true mode while PCs use inverted. It is a hardware thing that can not be fixed in soft ware . That is why we have SERIN/2, bit banging a "virtual serial poer".

I think the 3232 will also work but I have not used one to be sure about it.

If the module is always sending a 1,then use that in the WAIT part, grab what you need after that. What are the possibilities for the remaining data? 0-9-A-Z?

[Ioannis]

Dave, by 1 he means that the first bit of the first byte is "1" and the rest are first bit "0".

So wait cannot be used just like that.

unifoxz:
What is the repeat rate of the bytes? 8 bytes at 4800 and then a pause of some seconds or milliseconds?

You might just wait for the current transmission to finish, as you may have missed the begining of it, then wait for the pause state and grab the next 8 bytes.

But wait, you now say it is 5 bytes? At your first post I noticed you tried to get 8 bytes of data, right?

Ioannis

[unifoxz]

It's repeating 5 bytes. 5 bytes continued by another 5 bytes without pause, all are sent out continuously. In order to get the SpO2 byte and pulse rate byte which is at the 4th and 5th byte from the header byte (the byte with synchronous bit = 1), I need to read in 9 bytes as if the first byte I get is the 2nd byte of the 5 byte. So the header byte will be at the 5th byte and the SpO2 byte and pulse rate byte will be at the 8th byte and the 9th byte.

It's like this:
2, 3, 4, 5, 1 (header byte), 2, 3, 4 (pulse rate byte), 5 (SpO2 byte)

All the data is in hex format, no specific 0-9-A-Z.

[Ioannis]

I cannot imagine a device keep sending a blast of bytes without any synchronization!

Please give us a link for the data sheet or if small post it here.

Ioannis