On Fri 28 Nov, W.E. van Bemmel[SMTP:bemspan@XS4ALL.NL] wrote:
>
> If wheater allows I will use my lawnmower to chop the goat and ignite
> the barbecue by GPS controlled LASER.
>
> More seriously however, to stay [on topic],
>
> What is the virtue of slew rate limited RS485 devices like Maxim's 487
> compared
> to non-limited ones like MAX485, of which I have some samples?
> I can think of RFI, spikes, reflections...
>
> Who knows?

Slew-rate limited devices like the MAX487 have their edge rate decreased
to approx. 1us (5V/us).  This means that the highest radiated frequencies
are on the order of 1MHz instead of 40MHz, which greatly reduces EMI.
Additionally, the maximum unterminated cable length is approx
   L_max = 9 * t_r
due to reflections where t_r is the rise time in ns, and L_max is the
length in cm (90m for 1us).  This means that you can have long stubs on
your network -- and that makes it a lot easier to route cable.

Frank
------------------------------------------------------------------------
Frank A. Vorstenbosch                           Phone:  +44-181-636 3391
Electronics & Software Engineer                    or:  +44-181-636 3000
Eidos Technologies Ltd., Wimbledon, London      Mobile:  +44-976-430 569