HP 2641A Reference Manual page 66

YES
GO TO TRANSMIT
STATE. SEND
REQUEST TO
COMPUTER'
NO
YES
Data Communications
CALL
MONITOR
NO
R STU V
0000 0
GO BACK TO
RECEIVE
STATE
• A more detailed description
of this process is given in
Appendix C
SEND ACK
CHARACTER
RETURN
Figure 5-8. Reverse Channel Protocol
5-19