How to receive stream of bytes using PIC USART

[unifoxz]

The SpO2 module I use is of none parity.

I wonder the PIC have the problem to read the bytes if the bytes are sent into PIC in endless stream. I tried to send only 5 bytes, 10 bytes and 15 bytes data in SpO2 module's data format and the PIC can process well using the code I wrote.

Then I tried to let PIC sent out each byte it read in from a endless bytes stream. The output of the PIC is different from the data it read in.

[dhouston]

The SpO2 module I use is of none parity.

That's not the issue. How many STOP bits is the issue. If, as the only reference I could find for the BCI protocol says, it uses 8N2, you cannot handle it - all of the PBP methods require 1 stop bit. Two stop bits could explain the erratic results. You need to provide a link to the datasheet for the specific SP02 device you are using.

[Ioannis]

You need to provide a link to the datasheet for the specific SP02 device you are using.

I double that, although have asked for it earlier.

It seems you loose synchronization. But we are only guessing here as we have no informations about you device.

Ioannis

[unifoxz]

I try my best to translate the manual as the manual is originally written in Chinese language. The manual is too simple and not really provides the details.

serial port setting:

• 1 start bit + 8 data bit + 1 stop bit, no parity
• baud rate: 4800 baud
• 5 bytes format, 60 packages per second, bit 7 is the synchronous bit

byte 1:

• bit 7: synchronous bit, as 1
• bit 6: 1=instruction for pulse sound
• bit 5: 1=SpO2 decrease, 0=OK
• bit 4: 1=searching time too long, 0=OK
• bit 3-0: signal strength (0-8), represent signal strength of pulse

byte 2:

• bit 7: synchronous bit, as 0
• bit 6-0: pulse wave diagram

byte 3:

• bit 7: synchronous bit, as 0
• bit 6: pulse rate bit 7
• bit 5: 1=search pulse, 0=OK
• bit 4: 1=sensor error, 0=OK
• bit 3-0: pulse bar diagram

byte 4:

• bit 7: synchronous bit, as 0
• bit 6-0: pulse rate, (bit 6 to bit 0)

byte 5:

• bit 7: synchronous bit, as 0
• bit 6-0: SpO2

[dhouston]

OK - it has only one stop bit. It appears that various manufacturers use their own protocol.

60 packets per second x 5 bytes per packet x 10 bits per byte = 3000 bits per second which, at 4800bps, means 30 (or fewer - depends on pace) idle bit-times between packets.

I would capture 10 bytes, scan them for the first initial byte (>127) and then look at the following 4 bytes for your data.

EDIT: 9 bytes would guarantee one complete packet.

[Ioannis]

Hmm, seems that is like the pdf I posted. Is it the same module?

Based on the infos and the idea of Dave's:

array    var   byte[9]
temp    var   byte
i          var   byte
j          var   byte

get_new_data:
SerIn2 PORTB.7,16572,[str array\9]
for i=0 to 8
    temp=array[i]
    if temp.7=1 then goto send_at_9600
next i
hserout ["Not found!",13,10]
goto get_new_data

for j=i to i+4
hserout [array[j]]
next j

goto get_new_data

end

Hope this will get you started. Don't forget the defines for the Hserout command to set it at 9600.

Ioannis

[dhouston]

You need only scan the first five bytes to find the start of a packet. And you can save one step on each loop.

for i=7 to 39 STEP 8
    if array[0].i=1 then goto send_at_9600
next i