How to receive stream of bytes using PIC USART

[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

[dhouston]

Many devices send continuous blasts of data.

Here's a definition for spo2 http://www.neann.com/spo2.htm. A manual for the specific device would be helpful.

[Ioannis]

I did a little search in the web and found that the modules for medical applications use the so called BCI protocol with 4800 8-ODD-1 serial setup.

Data frames are 5 bytes long and on the first byte the 7th bit is 1 while on the restbit 7 is set to 0.

So, may be you get one byte at a time and check the bit 7 only for it to be 1. Then get the rest and store in a byte array of 5 elements.

If there is not a sync byte or a significant pause between frame transmissions, PIC cannot discriminate the start byte. That is why you get confussing results.

One untested example might be:

array    var   byte[5]
index    var   byte

index=0
get_new_data:
SerIn2 PORTB.7,16572,[B0]
if B0.7=1 then
    array[index]=B0
    index=index+1
endif

if index=5 then process_data

goto get_new_data

Ioannis

[dhouston]

I did a little search in the web and found that the modules for medical applications use the so called BCI protocol with 4800 8-ODD-1 serial setup.

Where did you find the protocol description? The only reference I found indicated it uses two stop bits.

[Ioannis]

Hi Dave. I found the attached pdf that is implying the protocol.

Ioannis

[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