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UM0193 Hardware
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1.2 RS-485 interface
The ST485A Transceiver ensures RS-485 communication through the UART1 serial
channel of the STR730F microcontroller as shown in
Figure 5 .
The maximum speed of this interface is greater than 30 Mbps.
A female, 9-pin D-Sub connector (J12) provides the RS-485 connection using a standard
Profibus pinout.
The RS-485 channel can be terminated using jumpers J10 and J13 as described in
Appendix C: Jumper settings . Terminating resistors R25, R26 and R28 are selected for a
Type-A Profibus DP cable as shown in Figure 5 . These resistors can be replaced with
different values depending on the physical layer implemented.
Figure 5. RS-485 schematic diagram
Table 2. RS-485 Connections
J12 Pin Signal STR730F MCU Peripheral
RxD (Receive Data) Port 2.9 UART1
TxD (Transmit Data) Port 2.8 UART1
DE (Driver Enable) Port 2.10 UART1
5 GND
1, 2, 4, 7 and 9 Not connected
Shielding Connected to GND by R31 || C26 (100 k
Ω
|| 4.7 nF)
Ai11694
5V
5V
5V
5V
TxD 485
RxD 485
nDE 485
R26 220R
NA
R2 220R
NA
R30 0R R30 0R
1 2
J10 J10
R28
390R
NA
R28
390R
NA
1 2
J13 J13
R29 0R R29 0R
1
J11 J11
R27
390R
R27
390R
1
2
3
4
5
6
7
8
9
M1
M2
J12 J12
RO
1
DI
4
GND 5
VCC 8
RE
2
DE
3
A 6
B 7
U4
ST485A
4
ST485A
R31 M1 R31 M1
C25
100n
C25
100n
R25
390R
NA
R25
390R
NA
C26
4n7/500V
C26
4n7/500V
DSUB9 - Socket