Advantech PCLS-848-P, User Manual

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9 0 PCLS-848-P User's Manual
9.8. Handshake lines
Each character byte transferred on the bus data lines employs the three wire hand-
shake sequence. This sequence has the following characteristics:
1) Data transfer is asynchronous. Data can be transferred at any rate suitable for the
devices operating on the bus. The devices wait for others to complete a byte
transfer.
2) Devices with different input and output speeds can be inter connected. Data
transfer rate is determined by the slowest active device.
3) Multiple devices can accept data at the same time.
The following definitions are used when discussing IEEE-488 bus:
1) SOURCE. A device sending information on the bus in either the command or data
mode.
2) TALKER. A device addressed to talk in the data mode.
3) ACCEPTOR. A device receiving information on the bUs in either the command
or data mode.
4) LISTENER. A device addressed to listen in the data mode.
The handshake lines have the following name and meaning:
DAV Data Valid
NRFD Not Ready For Data
NDAC Not Data Accepted
The handshake timing sequence is shown as following: