[edit] the title was changed to the below, but edit does not allow title changes[end edit]

this is NOT RS485, it is badly mutilated J1708

The fact you use a Rs485 chip does not make it RS485.

first you do not terminate.
second for low Tx you leave the line "open" (4k7 impedance).
third, you might as well connect DI to Vcc.
fourth you get RI signals when transmitting.
fifth, you need collision detection, not collision avoidance.

Basically you violate every rule there is not even a resemblance of RS485.

If you absolutely totally need to do without a direction pin use J1708.

If Harshada were communicating in close proximity, he might get by with what you suggest, but were that the case why would he want to change from RS232?

Anyhow Harshada indicated he switched to RS422 (using MAX488)

I strongly suggest you read "10 ways to bulletproof RS485" found via best serial appnotes in links.

Erik

for J1708 see fig 15 of
http://pdfserv.maxim-ic.com/en/ds/MAX...X3444E.pdf