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Mini57
Apr. 06, 2017
Page 306 of 475
Rev.1.00
MINI5
7
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TECH
NIC
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data is valid for transmission.
Shift Control
& Status
Control
TX_SFTR
Data
Serial Bus
Clock Input
Control Input
Shift Data
Output
TX_BUF
16
Transmit Buffer
Status
USCI_LINECTL
USCI_BUFSTS
USCI_TXDAT
Figure 6.11-6 Transmit Data Path
Transmit Data Validation
The status of TXEMPTY (USCI_BUFSTS[8]) indicates the transmission data is valid or not in the
transmit buffer (TX_BUF) and the TXSTIF (USCI_PROTSTS[1]) labels the start conditions for
each data.
If the USCI controller is a Master, the data transfer can only be started with valid data in the
transmit buffer (TX_BUF). In this case, the transmit shift register is loaded with the content
of transmit buffer.
Note:
Master defines the start of data transfer.
If the USCI controller is a Slave, a data transfer requested by Master and it has to be started
independently of the status in transmit buffer (TX_BUF). If a data transfer is requested and
started by the Master, the transmit shift register is loaded from specific protocol control
signal if it is valid for transmission.
Note:
Slave cannot define the start itself, but has to react.
The timing of loading data from transmit buffer to data shift unit depends on protocol
configurations.
UART:
A transmission of the data word in transmit buffer can be started if TXEMPTY = 0
in
normal operation.
SPI:
In Master mode, data transmission will be started when TXEMPTY (USCI_BUFSTS[8])
is 0. In Slave mode, the data transmission can be started only when slave selection signal is
at active state and clock is presented on USCIx_CLK pin.
I
2
C:
A transmission of the data byte in transmit buffer can be started if TXEMPTY = 0.
A transmission data which is located in transmit buffer can be started if the TXEMPTY
(USCI_BUFSTS [8]) = 0. The content of the transmit buffer (in TX_BUF condition) should
not be overwritten with new data while it is valid for transmission and a new transmission
can start. If the content of TX_BUF has to be changed, user can set TXRST (USCI_BUFCTL
[16]) to 1 to clear the content of TX_BUF before updating the data. Moreover, TXEMPTY
(USCI_BUFSTS [8]) will be cleared automatically when transmit buffer (TX_BUF) is updated
with new data. While a transmission is in progress, TX_BUF can be loaded with new data.
User has to update the TX_BUF before a new transmission.