Hi team,
My customer is using ISO35 and found an issue.
They have two kinds of modules which are using RS-485 bus to communicate with the ISO35 in another board.
Connecting with A module, ISO35 RXD could output signal correctly. But connecting with B module, ISO35RXD is muted, always high. RE is directly pulled low to GND.
We measured the high/low voltage in 485 bus. The voltages are all normal. And the data is as below
And the more strange thing is that if removing the parallel 300Ohm resistor across the A/B pin, the ISO35RXD could output signal correctly.
| 485 bus P | 485 bus N | RXD output | ||
| Module A | high level | 2.52 | 2.28 | Normal |
| low level | 1.32 | 1.16 | ||
| Module B | high level | 1.99 | 1.7 | No output |
| low level | 1.16 | 0.88 | ||
| Module B w/o 300Ohm resistor | high level | 2.04 | 1.72 | Normal |
| low level | 1.14 | 0.82 |
Could you give any idea what happened?
Thank you!
