HD64570 Datasheet, PDF (199/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

Receive data
Character
assembly
Sampling timing
Start bit search
Start bit check (space detected)
Space detected
(a) True Start Bit Detection
Receive data
Sampling timing
Start bit search
Start bit search
Start bit check (mark detected)
Space detected
(b) False Start Bit (Noise) Detection
Figure 5.18 Start Bit Sampling
Rev. 0, 07/98, page 183 of 453