User`s manual

CHAPTER 9 BUS TUTORIAL 71
9.8. Randshake 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 interconnected. Data
transfer rate is determined by the 3 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: