Strange extra hardware into a TT

Hello,

I have been given a TT with a bit of extra electronics: a little card with three components:
- a 74HC4040
- an oscillator 1.8 MHz
- a 16as15Hb1

It is soldered on the MFP68901 taking informations from four points:
- VCC
- Ground
- TC
- TC0

And it is also connected to a front LED.
Has anyone seen such a thing before?

Guillaume.