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Z51F6412
Product Specification
PS030302-0212
P R E L I M I N A R Y
100
11.7.8.3 Parity Generator
The Parity Generator calculates the parity bit for the sending serial frame data. When parity bit is
enabled (UPM[1]=1), the transmitter control logic inserts the parity bit between the MSB and the first
stop bit of the sending frame.
11.7.8.4 Disabling Transmitter
Disabling the Transmitter by clearing the TXE bit will not become effective until ongoing transmission
is completed. When the Transmitter is disabled, the TXD pin is used as normal General Purpose I/O
(GPIO) or primary function pin.
11.7.9 USART Receiver
The USART Receiver is enabled by setting the RXE bit in the UCTRLx1 register. When the Receiver
is enabled, the normal pin operation of the RXD pin is overridden by the USART as the serial input pin
of the Receiver. The baud-rate, mode of operation and frame format must be set before serial
reception. If synchronous or spi operation is used, the clock on the XCK pin will be used as transfer
clock. If USART operates in spi mode, SS pin is used as SS input pin in slave mode or can be
configured as SS output pin in master mode. This can be done by setting SPISS bit in UCTRLx3
register.
11.7.9.1 Receiving Rx data
When USART is in synchronous or asynchronous operation mode, the Receiver starts data
reception when it detects a valid start bit (LOW) on RXD pin. Each bit after start bit is sampled at pre-
defined baud-rate (asynchronous) or sampling edge of XCK (synchronous), and shifted into the
receive shift register until the first stop bit of a frame is received. Even if there’s 2
nd
stop bit in the
frame, the 2
nd
stop bit is ignored by the Receiver. That is, receiving the first stop bit means that a
complete serial frame is present in the receiver shift register and contents of the shift register are to
be moved into the receive buffer. The receive buffer is read by reading the UDATAx register.
If 9-bit characters are used (USIZE[2:0] = 7) the ninth bit is stored in the RX8 bit position in the
UCTRLx3 register. The 9
th
bit must be read from the RX8 bit before reading the low 8 bits from the
UDATAx register. Likewise, the error flags FE, DOR, PE must be read before reading the data from
UDATAx register. This is because the error flags are stored in the same FIFO position of the receive
buffer.
11.7.9.2 Receiver flag and interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) flag indicates whether there are unread data present in the receive
buffer. This flag is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty. If the Receiver is disabled (RXE=0), the receiver buffer is flushed and the RXC flag is
cleared.
When the Receive Complete Interrupt Enable (RXCIE) bit in the UCTRLx2 register is set and Global
Interrupt is enabled, the USART Receiver Complete Interrupt is generated while RXC flag is set.