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AT90S8414
Preliminary
4-51
Figure 42: UART Transmitter
Data transmission is initiated by writing the data to be transmitted to the UART I/O Data Register, UDR. Data is
transferred from UDR to the Transmit shift register when:
·
A new character has been written to UDR after the stop bit from the previous character has been shifted out. The
shift register is loaded immediately.
·
A new character has been written to UDR before the stop bit from the previous character has been shifted out. The
shift register is loaded when the stop bit of the character currently being transmitted has been shifted out.
If the 10(11)-bit Transmitter shift register is empty or when, data is transferred from UDR to the shift register. At this
time the UDRE (UART Data Register Empty) bit in the UART Status Register, USR, is set. When this bit is set (one), the
UART is ready to receive the next character. At the same time as the data is transferred from UDR to the 10(11)-bit shift
register, bit 0 of the shift register is cleared (start bit) and bit 9 or 10 is set (stop bit). If 9 bit data word is selected (the
CHR9 bit in the UART Control Register, UCR is set), the TXB8 bit in UCR is transferred to bit 9 in the Transmit shift
register.
On the Baud Rate clock following the transfer operation to the shift register, the start bit is shifted out on the TXD pin.
Then follows the data, LSB first. When the stop bit has been shifted out, the shift register is loaded if any new data has
been written to the UDR during the transmission. During loading, UDRE is set. If there is no new data in the UDR
register to send when the stop bit is shifted out, the UDRE flag will remain set. In this case, after the stop bit has been
present on TXD for one bit length, the TX Complete Flag, TXC, in USR is set.
Содержание AT90S8414
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Страница 6: ...4 6 AT90S8414 Preliminary Block Diagram Figure 1 The AT90S8414 Block Diagram...
Страница 65: ...AT90S8414 Preliminary 4 65 Figure 50 PORTB Schematic Diagram Pin PB5 Figure 51 PORTB Schematic Diagram Pin PB6...
Страница 68: ...4 68 AT90S8414 Preliminary Figure 53 PORTC Schematic Diagram Pins PC0 PC7...
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