It says IGNITION UNIT is this CDI

[Gra900]

I got this in the box of bits with my bike. Now mine is points, so a PO must have bought it.
If it’s any use to someone I would swap for something, maybe a set of down pipes, electronic ignition or beer vouchers.
It does look like someone has peered inside in the past

 

[xschris]

TCI ignition box use on 80-82 sohc xs400 bikes. (u.s.) That one looks like the first gen. 80 model 3F9. The 81-82(4R4) has less inside of it and more simple design.

 

[XSLeo]

CDI stands for Capacitive Discharge Ignition. This charges a big capacitor then discharges it through the coil to make spark.
TCI stands for Transistor Controlled Ignition. This uses a transistor to control the current flow through the coil. This is the same as points but uses a big transistor.
Leo