8520, 157 , 223 , 241 , 244 , 251 , 339 
  alarm, 344 
  handshaking, 341 
  input modes, 343 
  interval timers, 341 
    continuous, 342 
    force load, 342 
    one-shot, 342 
    PB on/off, 342 
    start/stop, 342 
    Toggle/pulse, 342 
  I/O ports, 341 
  read bit names, 343 
  register map, 340 
  signal assignments, 337 
  time-of-day clock, 344 
  write bit names, 343