Evaluation Kit Hardware
SAM3S-EK Development Board User Guide
4-5
11031A–ATARM–14-Dec-09
Note:
VDDPLL should be decoupled and filtered from VDDCORE.
4.3.6
UART
The Universal Asynchronous Receiver Transmitter features a two-pin UART that can be used for com-
munication and trace purposes. It offers an ideal channel for in-situ programming solutions. This UART
is associated with two PDC channels to reduce the processor time on packet handling.
This two-pin UART (TXD and RXD only) is buffered through an RS232 Transceiver MN6 and brought to
the DB9 male connector J7.
Figure 4-5.
UART
4.3.7
USART
The Universal Synchronous/Asynchronous Receiver Transmitter (USART) provides one full duplex uni-
versal synchronous/asynchronous serial link. The data frame format is extensively configurable (data
length, parity, number of stop bits) to support a broad range of serial communication standards. The
USART is also associated with PDC channels for TX/RX data access.
Note:
For design optimization purposes, both transmitters have been implemented on the same
PIO lines, that is PA21, 22, 23, 24 25.
To avoid any electrical conflict, the RS485 transceiver is isolated from the receiving line PA21.
Should you need to implement an RS485 channel in place of the RS232, follow the procedure below:
1.
make sure your software will permanently set PA23 to a high level - this will permanently disable the
RS232 receiver.
2.
solder a shunt resistor in place of R25 (a solder drop will do).
4.3.7.1
RS232
SAM3S-EK connects the USART1 bus (including TXD, RXD, RTS, CTS handshake signal controls and
EN command) to the DB9 male connector J5 through the RS232 Transceiver MN5.
+
3
V
3
DGND
DGND
+
3
V
3
+
3
V
3
FGND
PA10
PA9
C
3
9
100nF
C
3
9
100nF
C40
100nF
C40
100nF
TP5
S
MD
TP5
S
MD
J7
J7
5
4
3
2
1
9
8
7
6
10
11
R46
100K
R46
100K
C
38
100nF
C
38
100nF
TP6
S
MD
TP6
S
MD
C41
100nF
C41
100nF
R47
0R
R47
0R
R4
8
0R
R4
8
0R
C42
100nF
C42
100nF
MN6
MAX
3
2
3
2C
S
E
MN6
MAX
3
2
3
2C
S
E
T1IN
11
T2IN
10
R1OUT
12
R2OUT
9
T1OUT
14
T2OUT
7
R1IN
1
3
R2IN
8
V+
2
C1+
1
C1-
3
C2+
4
C2-
5
V-
6
VCC
16
GND
15
R45
100K
R45
100K
