Reddit mentions of Operating Systems Design and Implementat: Design and Implementation

According to the CP/M wikipedia page, you need the following to run it:

• A computer terminal using the ASCII character set
  
  
• An Intel 8080 (and later the 8085) or Zilog Z80 microprocessor
  
  
• At least 16 kilobytes of RAM (beginning at address 0)
  
  
• A means to bootstrap the first sector of the diskette
  
  
• At least one floppy disk drive
  
  So with the parts list above along with the UART should be enough to meet the requirements. You will need to use banked memory or a similar mechanism (since you need the bootstrap code at address 0, but CP/M needs RAM at address 0 as well). Only problem is the floppy drive, which you should be able to overcome with a Compact Flash card, an CF to IDE converter, and a IDE interface. I haven't tried this myself but I think something like this would work.
  
  If you were interested in writing your own OS, Operating Systems by Woodhull Tanenbaum is a good book on the topic.