How to receive stream of bytes using PIC USART

[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

[unifoxz]

Thanks for the suggestions, but the result I get is still not correct.

Have anyone tried to send an endless stream of bytes to PIC and then resend the stream back to PC? Will the input bytes same as the output bytes?