Adlink USB-3488A User Manual download pdf (Page 37)

Operation Theory 29

3.1.1 Data Lines

DIO1 to DIO8 carry both data and command messages. All com-

mands and most data use 7-bit ASCII codes, the 8th bit, DIO8, is

either unused or used as a parity check.

3.1.2 Handshake Lines

Three handshake lines control the transfer of data/messages

between devices.

 DAV (Data Valid): Indicates the condition (availability and

validity) of information on the DIO signal lines

 NRFD (Not Ready For Data): Indicates the condition of

readiness of the device(s) to accept data

 NDAC (Not Data Accepted): Indicates the condition of

acceptance of the data by the device

3.1.3 System Management Lines

Five system management lines manage the flow of control and

data bytes across the interface.

 EOI (End or Identify): Used (by a talker) to indicate the end

of a multi-byte transfer sequence or used in conjunction with

ATN (by a controller) to execute a polling sequence

 IFC (Interface Clear): Used (by a controller) to place the

interface system, portions of which are contained in all inter-

connected devices, in a known quiescent state

 SRQ (Service Request): Used by a device to indicate the

need for attention and to request an interruption of the cur-

rent sequence of events

 ATN (Attention): Used (by a controller) to specify how data

on the DIO signal lines are to be interpreted and which

devices must respond to the data

 REN (Remote Enable): Used (by a controller) in conjunction

with other messages to enable or disable one or more local

controls that have corresponding remote controls.

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Adlink USB-3488A User Manual Page 37