I'm using LT1487 RS485 chips to interconnect a PC with up to 120 8051 based smart transducers onto a single 4 core cable (Power, ground, "A" and "B" signals).

Since this is half duplex the PC disconnects from the "A" and "B" lines (bus??) after interogating each transducer so they can use the same lines to respond.

My question is how much delay should I put into the control signals to the LT1487's after the command codes have been sent to the 8051's (and vice-versa)?

The same question applies to how long should I wait after asserting the "A" and "B" lines before transmitting data onto these lines?

The "A" and "B" lines have been biased and terminated per the "10 rules for RS485" reference elsewhere on this Forum. The maximum distance from the PC to the furthest smart transducer is about 400 Meters. The comms from the PC are done with a Visual Basic program running under Win98, WinXP and Win2K.

All is working now with a single smart transducer but I'm using healthy 5mSec delays before and after asserting the buss. I would like to shorten these delays to the minimum and rather not rely on trial and error if someone can guide me.


Regards,

Bert van den Berg