ATA6613 ATMEL Corporation, ATA6613 Datasheet - Page 196

• Manufacturer Part Number: ATA6613
• Description: Ata6613
• Manufacturer: ATMEL Corporation

6.17.2.2
196
ATA6612/ATA6613
Double Speed Operation (U2Xn)
Table 6-71
ing the UBRRn value for each mode of operation using an internally generated clock source.
Table 6-71.
Note:
Some examples of UBRRn values for some system clock frequencies are found in
page 218
page
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit only has
effect for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling
the transfer rate for asynchronous communication. Note however that the Receiver will in this
case only use half the number of samples (reduced from 16 to 8) for data sampling and clock
recovery, and therefore a more accurate baud rate setting and system clock are required when
this mode is used. For the Transmitter, there are no downsides.
Operating Mode
Asynchronous Normal mode
(U2Xn = 0)
Asynchronous Double
Speed mode (U2Xn = 1)
Synchronous Master mode
218).
BAUD
f
UBRRn
OSC
1. The baud rate is defined to be the transfer rate in bit per second (bps)
(see
contains equations for calculating the baud rate (in bits per second) and for calculat-
Equations for Calculating Baud Rate Register Setting
“Examples of UBRRn Settings for Commonly Used Oscillator Frequencies” on
Baud rate (in bits per second, bps)
System Oscillator clock frequency
Contents of the UBRRnH and UBRRnL Registers, (0-4095)
Equation for Calculating Baud
BAUD
BAUD
BAUD
=
=
=
----------------------------------------- -
16 UBRRn
Rate
-------------------------------------- -
8 UBRRn
-------------------------------------- -
2 UBRRn
(1)
f
f
f
OSC
OSC
OSC
+
+
+
1
1
1
UBRRn
UBRRn
UBRRn
Equation for Calculating UBRRn
=
=
=
----------------------- - 1
16BAUD
------------------- - 1
8BAUD
------------------- - 1
2BAUD
f
f
f
OSC
OSC
Value
OSC
9111C–AUTO–02/08
–
–
Table 6-79 on
–