AT90S/LS4434 and AT90S/LS8535
58
UART Control Register – UCR
•
Bit 7 – RXCIE: RX Complete Interrupt Enable
When this bit is set (one), a setting of the RXC bit in USR will cause the Receive Complete Interrupt routine to be executed
provided that global interrupts are enabled.
•
Bit 6 – TXCIE: TX Complete Interrupt Enable
When this bit is set (one), a setting of the TXC bit in USR will cause the Transmit Complete Interrupt routine to be executed
provided that global interrupts are enabled.
•
Bit 5 – UDRIE: UART Data Register Empty Interrupt Enable
When this bit is set (one), a setting of the UDRE bit in USR will cause the UART Data Register Empty Interrupt routine to be
executed provided that global interrupts are enabled.
•
Bit 4 – RXEN: Receiver Enable
This bit enables the UART receiver when set (one). When the receiver is disabled, the RXC, OR and FE status flags cannot
become set. If these flags are set, turning off RXEN does not cause them to be cleared.
•
Bit 3 – TXEN: Transmitter Enable
This bit enables the UART transmitter when set (one). When disabling the transmitter while transmitting a character, the
transmitter is not disabled before the character in the shift register plus any following character in UDR has been com-
pletely transmitted.
•
Bit 2 – CHR9: 9 Bit Characters
When this bit is set (one), transmitted and received characters are 9 bits long, plus start and stop bits. The ninth bit is read
and written by using the RXB8 and TXB8 bits in UCR, respectively. The ninth data bit can be used as an extra stop bit or a
parity bit.
•
Bit 1 – RXB8: Receive Data Bit 8
When CHR9 is set (one), RXB8 is the ninth data bit of the received character.
•
Bit 0 – TXB8: Transmit Data Bit 8
When CHR9 is set (one), TXB8 is the ninth data bit in the character to be transmitted.
Baud Rate Generator
The baud rate generator is a frequency divider which generates baud rates according to the following equation:
• BAUD = Baud rate
• f
CK
= Crystal clock frequency
• UBRR = Contents of the UART Baud Rate register, UBRR (0 - 255)
For standard crystal frequencies, the most commonly used baud rates can be generated by using the UBRR settings in
Table 25. UBRR values that yield an actual baud rate differing less than 2% from the target baud rate are boldface in the
table. However, using baud rates that have more than 1% error is not recommended. High error ratings give less noise
resistance.
Bit
7
6
5
4
3
2
1
0
$0A ($2A)
RXCIE
TXCIE
UDRIE
RXEN
TXEN
CHR9
RXB8
TXB8
UCR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R
W
Initial value
0
0
0
0
0
0
1
0
BAUD
f
CK
16(UBRR
1
)
+
--------------------------------------
=