Isosynchronous baud value =
For BAUD = 0,
Isosynchronous baud value =
VCLK Frequency
BAUD 1+
-----------------------------------------------------------------
VCLK Frequency
32
-------------------------------------------------
Asynchronous baud value =
For BAUD = 0,
Asynchronous baud value =
VCLK Frequency
16 * (BAUD + 1)
-----------------------------------------------------------------
VCLK Frequency
32
-------------------------------------------------
SCI Communication Formats
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SPNU563A–March 2018
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Serial Communication Interface (SCI) Module
30.2.3 SCI Baud Rate
The SCI has an internally generated serial clock determined by the peripheral VCLK and the prescalers
BAUD. The SCI uses the 24-bit integer prescaler BAUD value in the BRS register to select the required
baud rates.
In asynchronous timing mode, the SCI generates a baud clock according to the following formula:
(57)
In isosynchronous timing mode, the SCI generates a baud clock according to the following formula:
(58)
30.2.4 SCI Multiprocessor Communication Modes
In some applications, the SCI may be connected to more than one serial communication device. In such a
multiprocessor configuration, several frames of data may be sent to all connected devices or to an
individual device. In the case of data sent to an individual device, the receiving devices must determine
when they are being addressed. When a message is not intended for them, the devices can ignore the
following data. When only two devices make up the SCI network, addressing is not needed, so
multiprocessor communication schemes are not required.
SCI supports two multiprocessor Communication Modes which can be selected using COMM MODE bit:
• Idle-Line Mode
• Address Bit Mode
When the SCI is not used in a multiprocessor environment, software can consider all frames as data
frames. In this case, the only distinction between the idle-line and address-bit modes is the presence of an
extra bit (the address bit) in each frame sent with the address-bit protocol.
The SCI allows full-duplex communication where data can be sent and received via the transmit and
receive pins simultaneously. However, the protocol used by the SCI assumes that only one device
transmits data on the same bus line at any one time. No arbitration is done by the SCI.
NOTE: Avoid Transmitting Simultaneously on the Same Serial Bus
The system designer must ensure that devices connected to the same serial bus line do not
attempt to transmit simultaneously. If two devices are transmitting different data, the resulting
bus conflict could damage the device..
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