From: Oliver Broad Subject: Re: [PIC]: Commx with half duplex RS485 > For what it's worth I believe a lot depends on what the bus turnaround > time is. Some microcontroller to microcontroller apps use near instant > turnaround but sometimes delays of 100ms or more are added between > recieving and replying to give the host time to turn the port round. > In our case it was 9ms. Easy for DOS but not Windows. Personally I > strongly doubt it is possible to switch the port reliably at > application level as your program might not even be active the instant > the data goes out. When confronted with this problem I specified: > Right now I have about 10ms turnaround time, but I think I will increase this time, reviewing the answers I have got so far. > 1. A 'magic' interface for testing which senses the data going out and > sets the direction accordingly. Significantly the time delay before > release was less than a bit, so it was necessary to bias the bus to a > '1' state to prevent corruption. This oddity makes me wary of this > method in finished installations. > > 2. A standard interface requiring soft direction control, but with a > device driver supporting RS485 direction control. The one we used from > Amplicon supported both internal 485 and an external converter, the > difference being the different lines used to enable transmission. > Interesting, I will look into this Amplicon device driver, thanks. ============================== Ruben Jvnsson AB Liros Elektronik Box 9124, 200 39 Malmv, Sweden TEL INT +46 40142078 FAX INT +46 40947388 ruben@pp.sbbs.se ============================== -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu