
  | 
  | CHAPTER 4: Operation | 
Data Flow —  | ||
Bisynchronous Device | Asynchronous Device  | |
Send data block D
NAK
Send data block D
ACK 0
when available
Send block D
If data not properly received by 
Send data block E
NAK
Retransmit block E
ACK 1 (when
correctly received)
Send block E
If data not yet available from synchronous device while synchronous line to 
TTD
NAK
TTD
NAK
Continues until data available
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