ADLINK USB-3488A - Manual (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.