STIR4200 SigmaTel, STIR4200 Datasheet - Page 12

• Manufacturer Part Number: STIR4200
• Description: USB / IrDA Bridge Controller
• Manufacturer: SigmaTel

STIr4200
USB/IrDA Bridge Controller
12
5.1.3.
Receive Frame Format
Data received into the STIr4200 FIFO from the digital infrared interface can be
accessed by performing a bulk read on the USB interface. The received data con-
tains the encoded infrared data. The STIr4200 does not perform any frame valida-
tion or CRC-Checking. Multiple frames may exist within one bulk read depending
upon the size of the bulk read. However, the end of the bulk read buffer may not
necessarily coincide with the end of an infrared frame. It is highly likely that the data
at the end of a bulk read will be a partial frame. The remaining frame data will be
acquired in the next bulk read.
The bulk data thus contains start-of-frame (BOF) characters, end-of-frame (EOF)
characters, and escape characters that delineate the actual frame. It is the responsi-
bility of the host software to reconstruct the frame.
5.1.3.1.
The standard SIR encoding scheme provides all information needed to delineate
the encoded receive frames. Figure 6 summarizes the SIR receive frame format
encoding scheme.
MSB CRC
LSB CRC
0xC0
0xC0
0xC0
0xC0
0xC0
0xC1
Data
Data
Data
Data
Data
Data
Data
…
…
SIR Receive Frame
Figure 6. SIR Receive Frame Format
BOF = Beginning of frame characters
The number of beginning of frame
characters is determined during the
negotiation stage.
Address/Control/Information Fields
Special characters have been escaped. Software
must un-escape the data
EOF - End of frame
FCS : 16 bit CRC-CCITT
Escaped Data
0x7D 0xE0
0x7D 0xE1
0x7D 0x5D
A
C
Original Data
0xC0
0xC1
0x7D
I
Original Data
0xC0
0xC1
0x7D
3-4200-D1-2.0-0403