Can't control anything past channel 51.

[Giovanni Intini]

Hi, I have 10 tube with 16 led rgb lamps, connected between them with
a serial connection. They work fine with different kinds of USB DMX
controllers (like ENTTEC DMX USB PRO).

I built a DMX shield and connected it to Arduino and then tried using
DmxSimple to control the lamps. Unfortunately I can't control anything
past channel 51 (1 led of the second bar). The rest of the leds of the
second bar behave erratically while the other eight bars keep looping
in their rgb demo, as if no one is sending any kind of signal to them.

I feared my DMX shield was not ok so I had a friend of mine build one
and he connected it to his lamps, and he gets exactely the same
problem, can't do anything past channel 51.

He played a bit with DmxSimple.cpp changing the timings in
ISR(TIMER2_OVF_vect,ISR_NOBLOCK) {...} and with a lot of trial and
error he can control up to channel 70, but can't go past that.

Any clue? This thing is really driving me mad.