I want to use an external clock source (a 12MHz TCXO) fed into the XTALIN pin of the LPC11C12 microcontroller. This could either be as a clipped sine wave (0.8V peak to peak, no negative swing) directly from the TCXO, or I could put it through a schmitt trigger to get a digital input at whatever voltage level. I read in the datasheet that to do this I should put the XTALIN pin into bypass mode (pg 29 of user manual) to allow this, but there is no mention of required voltage level/duty cycle/digital or sine input etc.
The user manual only says (at multiple points) with relation to the XTALIN pin - "Input to the oscillator circuit and internal clock generator circuits. Input voltage must not exceed 1.8 V.", but nothing else.
Could anyone help me with this?