TTL to 485 converter

Hello Guys,

I've posted several topics on here but i don't know how to find the previous ones.

I am using a TTL to 485 converter and i'm experiencing some problems. My converter works WITHOUT enabling the transmit pin. also, if i put a scope on the enable pin when only giving it a power supply, there is a voltage of 5V on this pin, so appearantly the board makes the pins HIGH by just supplying power.

this way i can't get it in receive mode and thus it is not working. has any of you experienced this before? i think i just need to get a new converter.

maybe you have a different idea on this.

Jan-Jelle

Maybe the TTL to RS485 converter has a pull up resistor to pull the enable pin high, and you have to pull it low to disable it.

If you gave use more details such as the make / model then we could be of more assistance

Hello John,

Yes you are right on the money. I took a look at the schematics and the DE and RE pins have pull up resistors. I pulled these off and it worked fine!!

pulling the port low wasn't sufficient enough for proper data transmit, so i had to remove the resistors. I don't know why pulling it low was not good enough. if you write a digital port low, is it hooked straight to ground internally?

Thanks for the advice!

if you write a digital port low, is it hooked straight to ground internally?

Well, connected to Gnd thru a transistor. Others have suggested an on resistance of around 40 ohm.