5v Pin For MAX485 Current

How much current can the onboard 5v regulator source? Planning to use a MAX485 for DMX control and using the onboard 5v to supply it but concerned with current capability (max draw on the MAX is 700+ mA) and injecting noise from the MAX485 onto the main Arduino 5v bus.

Should I use a separate 5v regulator off the 9v supplying the Arduino to supply the MAX485?

700mA? I don't see that number anywhere in the data sheet http://datasheets.maximintegrated.com/en/ds/MAX1487-MAX491.pdf Largest current draw is with a shorted output, and that is 250mA. Regulator is good for up to 800mA, but only if the voltage in is fairly low, like 6.5-7.5V, otherwise it will overheat and shut down.

Oops ... The 700+ was power dissipation not current. Hadn't had my coffee yet!

Think the MAX485 should have its own supply or use Arduino's? I don't know how much noise it'll induce on 5v line when transmitting DMX (200kHZ).

Well,the 200KHz is coming from the Atmega to start at 0/5V levels, the 485 is buffering and sending out a balanced signal at the same rate. You shouldn't see a problem running from the same supply. Be sure to put a 0.1uF/100nF decoupling caps on the 485 VCC pin, mounted near the pin.