What has happened to the UCN5804?
From http://www.allegromicro.com/en/Products/Part_Numbers/Archive/index.asp:


  5804: BiMOS II Unipolar Stepper-Motor
  Translator/Driver
  
  http://www.allegromicro.com/en/Products/Part_Numbers/Archive/5804.pdf
  
  discontinued October 2004; replaced by
  A3967 and A3977