Uart Via Rs-232 - mikroElektronika EasyAVR v7 User Manual

UART via RS-232

Enabling RS-232
In order to enable RS-232
communication, you must set
J23 and J12 jumpers in the RS-
232 position, and enable desired
RX and TX lines via SW10 DIP
switch. For example, if you want
to enable RS-232 connection
on UART module of the default
ATmega32 chip, you should
SW10.1
enable (RD0) and
SW10.2 (RD1) lines.
DATA BUS
RX-232
RX-FTDI
J23 RX
TX
TX-232
SW10
TX-FTDI
J12
TX-232
RX-232
page 14
The UART (universal asynchronous
receiver/transmitter) is one of the most
common ways of exchanging data between
the MCU and peripheral components. It is
a serial protocol with separate transmit and
receive lines, and can be used for full-duplex
communication. Both sides must be initialized with
the same baud rate, otherwise the data will not be
received correctly.
RS-232 serial communication is performed through a
9-pin SUB-D connector and the microcontroller UART
module. In order to enable this communication, it
is necessary to establish a connection between
RX and TX lines on SUB-D connector and the
same pins on the target microcontroller using
DIP switches. Since RS-232 communication
voltage levels are different than
microcontroller logic levels, it is
necessary to use a RS-232
Transceiver circuit, such as
MAX3232 as shown
on Figure 6-1.
U3
1
C1+
2
C11 V+
100nF
3
C1-
PD0 4
C2+
PD1
C20
5
PD2
100nF C2- C2-
PD3
6
V-
V-
7
T2OUT
8
R2IN
MAX3232
C21 C22
100nF 100nF
VCC-BRD
VCC-BRD VCC-BRD
16 E2
VCC
10uF
15
GND
14
T1OUT
13
R1IN
12
R1OUT
11
T1IN
10
T2IN
9
R2OUT
R35
100K
Figure 6-1: RS-232 connection schematic
CN12
1
6
2
7
3
8
4
9
5
DB-9
EasyAVR
v7