atmega323l ATMEL Corporation, atmega323l Datasheet - Page 90

• Manufacturer Part Number: atmega323l
• Description: Atmega323 8-bit Avr Microcontroller With 32k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

90
ATmega323(L)
R
Table 30 and Table 31 list the maximum Receiver baud rate error that can be tolerated.
Note that normal speed mode has higher toleration of baud rate variations.
Table 30. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode
(U2X = 0)
Table 31. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode
(U2X = 1)
The recommendations of the maximum Receiver baud rate error was made under the
assumption that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the Receivers baud rate error. The Receiver’s sys-
tem clock (XTAL) will always have some minor instability over the supply voltage range
and the temperature range. When using a crystal to generate the system clock, this is
rarely a problem, but for a resonator the system clock may differ more than 2% depend-
ing of the resonators tolerance. The second source for the error is more controllable.
The baud rate generator can not always do an exact division of the system frequency to
get the baud rate wanted. In this case an UBRR value that gives an acceptable low error
can be used if possible.
(Data+Parity Bit)
slow
# (Data+Parity
is the ratio of the slowest incoming data rate that can be accepted in relation to the
Receiver baud rate. R
accepted in relation to the Receiver baud rate.
Bit)
10
D #
D
5
6
7
8
9
10
5
6
7
8
9
R
R
slow
93.20
94.12
94.81
95.36
95.81
96.17
slow
94.12
94.92
95.52
96.00
96.39
96.70
(%)
(%)
fast
is the ratio of the fastest incoming data rate that can be
R
106.67
105.79
105.11
104.58
104.14
103.78
fast
(%)
R
105.66
104.92
104.35
103.90
103.53
103.23
fast
(%)
+5.79/-5.88
+5.11/-5.19
+4.58/-4.54
+4.14/-4.19
+3.78/-3.83
Max Total
+6.67/-6.8
Error (%)
+5.66/-5.88
+4.92/-5.08
+4.35/-4.48
+3.90/-4.00
+3.53/-3.61
+3.23/-3.30
Max Total
Error (%)
Recommended Max
Receiver Error (%)
Recommended
Max Receiver
± 2.5
± 2.0
± 2.0
± 1.5
± 1.5
± 3.0
Error (%)
1457G–AVR–09/03
± 2.5
± 2.0
± 1.5
± 1.5
± 1.5
± 1.0