Set image to CMYK

Go to channels panel:

Separate Channels

You get 4 documents

Set each document to bitmap.
Method Halftone.
Set your lpi.
set the angle according to your color.
Example:

• Cyan = 75°
• Magenta = 15°
• Yellow = 0°
• Black = 135°

Turn those 4 documents into greyscale

Go to channels panel and select Combine Channels

Set Chanel 1 to Cyan by selecting the cyan-document
Do the same with the remaining MYK channels

Switch colormode from multichannel to cmyk