Lpc2000

>>Does anyone know what is the maximum speed that I could send
>>data to the D/A at fixed frequency?

You can eliminate the software jitter by introducing a set of
latches.

Use the hardware timer or PWM hardware to generate a fixed
frequency square-wave (or edge at least) on an output pin.
Use this to latch the input to the DAC.

In your software, triggered from the same timer, write the
next valid sample to the input of the latch, eg. on the
output pins of the micro, or to another latch that
preceeds the DAC latch.

The software jitter then only affects the data written
to the first latch, data written to the second latch
(or DAC internal latch) is done by the timer I/O pin,
so is unaffected by the software jitter.

If you use software to fill a FIFO, then the DAC can be
driven by the FIFO draining, and software can fill it
up on an 'almost empty' interrupt. You'll get higher
performance from the DAC with this scheme.

Cheers
Dave