AT94K05AL-25BQX Atmel, AT94K05AL-25BQX Datasheet - Page 138

• Manufacturer Part Number: AT94K05AL-25BQX
• Manufacturer: Atmel

Specifications of AT94K05AL-25BQX

• Device System Gates: 5000
• Propagation Delay Time: 12.1ns
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Operating Supply Voltage (min): 3V
• Operating Temperature Classification: Commercial
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Mounting: Surface Mount
• Pin Count: 144
• Package Type: LQFP
• Lead Free Status / RoHS Status: Compliant

4.29.6
4.29.7
138
AT94KAL Series FPSLIC
Double Speed Transmission
The Baud-rate Generator in Double UART Speed Mode
UART0 Baud-rate Register Low Byte – UBRR0
UART1 Baud-rate Register Low Byte – UBRR1
UBRRn stores the 8 least significant bits of the UART baud-rate register.
The FPSLIC provides a separate UART mode that allows the user to double the communication
speed. By setting the U2X bit in UART Control and Status Register UCSRnA, the UART speed
will be doubled. The data reception will differ slightly from normal mode. Since the speed is dou-
bled, the receiver front-end logic samples the signals on the RXDn pin at a frequency 8 times the
baud-rate. While the line is idle, one single sample of logic 0 will be interpreted as the falling
edge of a start bit, and the start bit detection sequence is initiated. Let sample 1 denote the first
zero-sample. Following the 1-to-0 transition, the receiver samples the RXDn pin at samples 4, 5
and 6. If two or more of these three samples are found to be logic 1s, the start bit is rejected as
a noise spike and the receiver starts looking for the next 1-to-0 transition.
If however, a valid start bit is detected, sampling of the data bits following the start bit is per-
formed. These bits are also sampled at samples 4, 5 and 6. The logical value found in at least
two of the three samples is taken as the bit value. All bits are shifted into the transmitter shift reg-
ister as they are sampled. Sampling of an incoming character is shown in
Figure 4-44. Sampling Received Data when the Transmission Speed is Doubled
Note that the baud-rate equation is different from the equation
speed is doubled:
Note:
For standard crystal frequencies, the most commonly used baud-rates can be generated by
using the UBR settings in
than 1.5% from the target baud-rate, are bold in the table. However since the number of samples
Bit
$09 ($29)
Read/Write
Initial Value
Bit
$00 ($20)
Read/Write
Initial Value
• BAUD = Baud-rate
• f
• UBR = Contents of the UBRRHI and UBRRn Registers, (0 - 4095)
CK
SAMPLING
RECEIVER
= Crystal Clock Frequency
RXD
1. This equation is only valid when the UART transmission speed is doubled.
START BIT
7
MSB
R/W
0
7
MSB
R/W
0
D0
6
R/W
0
6
R/W
0
Table
D1
5
R/W
0
5
R/W
0
2. UBR values which yield an actual baud-rate differing less
BAUD
D2
4
R/W
0
4
R/W
0
=
----------------------------- -
8(UBR
D3
3
R/W
0
3
R/W
0
f
CK
+
D4
1 )
2
R/W
0
2
R/W
0
D5
(1)
at
1
R/W
0
1
R/W
0
page 136
D6
Figure
0
LSB
R/W
0
0
LSB
R/W
0
D7
when the UART
4-44.
1138I–FPSLI–1/08
STOP BIT
UBRR0
UBRR1