
Serial communications interface (SCI) ST72321xx-Auto
138/243 Doc ID 13829 Rev 1
15.4 Functional description
The block diagram of the Serial Control Interface, is shown in Figure 62. It contains six
dedicated registers:
● 2 control registers (SCICR1 and SCICR2)
● a status register (SCISR)
● a baud rate register (SCIBRR)
● an extended prescaler receiver register (SCIERPR)
● an extended prescaler transmitter register (SCIETPR)
Refer to the register descriptions in Section 15.7 for the definitions of each bit.
15.4.1 Serial data format
Word length may be selected as being either 8 or 9 bits by programming the M bit in the
SCICR1 register (see Figure 62).
The TDO pin is in low state during the start bit.
The TDO pin is in high state during the stop bit.
An Idle character is interpreted as an entire frame of ‘1’s followed by the start bit of the next
frame which contains data.
A Break character is interpreted on receiving ‘0’s for some multiple of the frame period. At
the end of the last break frame the transmitter inserts an extra ‘1’ bit to acknowledge the
start bit.
Transmission and reception are driven by their own baud rate generator.
Figure 63. Word length programming
Bit0
Bit1
Bit2
Bit3
Bit4
Bit5
Bit6
Bit7
Bit8
Start
Bit
Stop
Bit
Next
Start
Bit
Idle Frame
Bit0
Bit1
Bit2
Bit3
Bit4
Bit5
Bit6
Bit7
Start
Bit
Stop
Bit
Next
Start
Bit
Start
Bit
Idle Frame
Start
Bit
9-bit Word length (M bit is set)
8-bit Word length (M bit is reset)
Possible
Parity
Bit
Possible
Parity
Bit
Break Frame
Start
Bit
Extra
‘1’
Data Frame
Break Frame
Start
Bit
Extra
‘1’
Data Frame
Next Data Frame
Next Data Frame
Komentáře k této Příručce