AN3975

System implementation - HW

Doc ID 022170 Rev 1

9/26

Figure 5 shows the physical implementation and signal pinout listed in Table 1 of the RS485

module. Outputs of the RS485 driver, the RS485 bus, are bonded to the connector depicted

on the right in Figure 5. The RS485 bus has two lines named A and B. The common ground

is also bonded out at the same connector. Two coupling capacitors 10 µF and 100 nF are

connected between +5 V and GND. We recommend adding 1 k

Ω serial resistors to the

signals between the microcontroller board CG and RS485 driver (namely, signals RO, RE,

DE, DI) during the debugging phase in order to avoid damage of used chips. The resistors

are not necessary and can be removed once the application works as expected.

Figure 5.

Module signal pinout

1.

Signal +5 V is connected to the bottom pin of the header.

Table 1.

Signals of interconnection of STEVAL-PCC012V1 and RS485 module

Signal

CN3 (CG)

RS485

USART_RX

DAC_STBY - PD6 - PIN 15

R0

GPIO

STBY_R - PD4 - PIN11

RE

GPIO

SPK_STBY - PD7 - PIN17

DE

USART_TX

STBY_L - PD5 - PIN13

DI

+5 V

PIN 2

GND

PIN 19

GND