Advantech PCL-848A/B Manuel d'utilisateur télécharger pdf (Page 77)

CHAPTER 9

BUS TUTORIAL

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:

1 2 ... 72 73 74 75 76 77 78 79 80 81 82 83 84

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Advantech PCL-848A/B Manuel d'utilisateur Page 77