EIA-485 driver and receiver enables

Hi,

I've been looking through on-line material for an application note that ties the driver enable and receiver enable (negative active) together (for say a DS3695AT) which is then controlled by a uProcessor for half duplex interfaces, but have not found one.  I'd like to assume I can, but is there any timing constraint in doing so? I'm also assuming that for an idle condition one would leave the driver disabled and the receiver enabled.  Or for a full duplex device, such as a SN751177, can I tie them directly to VCC and GND and leave them enabled permanently?

Thanks.
Marty