On-chip peripherals
ST72344xx, ST72345xx
Character transmission
During an SCI transmission, data shifts out least significant bit first on the TDO pin. In
this mode, the SCIDR register consists of a buffer (TDR) between the internal bus and
Procedure:
–
Select the M bit to define the word length.
–
Select the desired baud rate using the SCIBRR and the SCIETPR registers.
–
Set the TE bit to send an idle frame as first transmission.
–
Access the SCISR register and write the data to send in the SCIDR register (this
sequence clears the TDRE bit). Repeat this sequence for each data to be
transmitted.
Clearing the TDRE bit is always performed by the following software sequence:
a)
An access to the SCISR register
b)
A write to the SCIDR register
The TDRE bit is set by hardware and it indicates:
–
The TDR register is empty.
–
The data transfer is beginning.
–
The next data can be written in the SCIDR register without overwriting the
previous data.
This flag generates an interrupt if the TIE bit is set and the I bit is cleared in the CCR
register.
When a transmission is taking place, a write instruction to the SCIDR register stores
the data in the TDR register and which is copied in the shift register at the end of the
current transmission.
When no transmission is taking place, a write instruction to the SCIDR register places
the data directly in the shift register, the data transmission starts, and the TDRE bit is
immediately set.
When a frame transmission is complete (after the stop bit or after the break frame) the
TC bit is set and an interrupt is generated if the TCIE is set and the I bit is cleared in the
CCR register.
Clearing the TC bit is performed by the following software sequence:
a)
An access to the SCISR register
b)
A write to the SCIDR register
Note:
The TDRE and TC bits are cleared by the same software sequence.
Break characters
Setting the SBK bit loads the shift register with a break character. The break frame
As long as the SBK bit is set, the SCI send break frames to the TDO pin. After clearing
this bit by software the SCI insert a logic 1 bit at the end of the last break frame to
guarantee the recognition of the start bit of the next frame.
Idle characters
Setting the TE bit drives the SCI to send an idle frame before the first data frame.
Clearing and then setting the TE bit during a transmission sends an idle frame after the
current word.