AN3975

Tests

Doc ID 022170 Rev 1

19/26

6.3

Sending short data from HyperTerminal to RS485 bus not

using matching resistor

Figure 13 shows the influence of disconnection of the matching resistor on RS485 bus lines.

Figure 13.

RS485 - two-byte transmission - jumper J1 opened, matching resistor 120

not connected

6.4

Closed loop communication test of 320-byte message

In order to test the whole transparent link before involving the RS485 device, e.g. power

meter and automated meter reading SW on the PC side, it is necessary to perform a test

that proves the whole chain is working.

Closed loop communication test can be performed by two approaches:

●

FW: It can be switched on by changing the FW. See Appendix A with guidance on how

to update the project file in order to enable closed loop test - see Figure 14.

●

HW: It can be switched on by changing the HW. The RS485 module should be removed

from the CN3 connector of the CG of the power meter part. According to Table 1, the

USART_TX and USART_RX must be interconnected by a wire - see Figure 15.