AN969 Datasheet, PDF (3/10 Pages) STMicroelectronics – SCI COMMUNICATION BETWEEN ST7 AND PC

SCI COMMUNICATION BETWEEN ST7 AND PC
1.3 FRAMES
Any transmission is Least Significant Bit first. A data word can be 8 or 9 bits long. A data frame
begins with a «start bit», which is a ’0’ bit and ends with a «stop bit», which is a ’1’ bit. See
Figure 2.
Two special frames are also managed :
An Idle character is interpreted as an entire frame of ’1’ bits followed by the start bit of the next
frame which contains data.
A Break character is detected when receiving ’0’ bits for some multiple of the frame period. At
the end of the last break, the transmitter inserts an extra ’1’ bit to acknowledge the next start
bit.
Figure 2. Frames and word length
9-bit Word length (M bit of SCICR1 is set)
Data Frame
Start
Bit Bit0 ^{Bit1 Bit2 Bit3} Bit4 ^{Bit5 Bit6}
Bit7 Bit8
Next Data Frame
Next
Stop
Bit
Start
Bit
Idle Frame
Start
Bit
Break Frame
Extra ^Start
’1’ ^Bit
8-bit Word length (M bit of SCICR1 is reset)
Data Frame
Start
Bit Bit0 Bit1 ^Bit2 Bit3 Bit4 ^{Bit5 Bit6}
Next Data Frame
Next
Bit7
Stop
Bit
Start
Bit
Idle Frame
Start
Bit
Break Frame
Extra
’1’
Start
Bit
3/10