IEEE 488 Programmable Interface

This interface is for Programmable Instrumentation   using a Data Bus between instruments to transfer data to and from the various instruments connected.

The interface uses voltage levels of +5V DC for logical 0 (False) and pulls this to ground for logic 1 (True) . Devices on the bus are called GPIB Devices (General Purpose Interface Bus !! I Think!!) and can be one of three types

1. Talker       : a device configured to allow it to put data on the bus , transmitting  data to one or more other devices. There may be only one talker active any one time.
   
2. Listener    : this accepts data from the bus using handshaking signals . There may be more than 1 listener active at any one time .
   
3. Controller  : The controller is the only device on the bus capable of asserting the ATN line which tells all the devices on the bus to get ready to receive commands. There is only one controller active at a time in the system . When two or more controllers are connected to the bus then control must be passed from one to the other.

Bus structure

The control lines define how the data on the D101 -D108 is to be interpreted.

IFC (Interface Clear)

• Used by Controller to put all the deices in a quiet state .

SRQ (Service Request)

• Asserted by a device when it requires a service sequence.

REN ( Remote Enable)

• When REN is asserted by the Controller the listener will ignore its front panel controls.

EOI (End or Identify) 

This line has two functions :

• END     : Asserted by a talker to indicate the end of a multi-byte message.
• Identify : Asserted by controller with the ATN line when conducting a parallel poll.

• Data Valid : Asserted by controller to indicate it has put a Control byte on the bus.

• Not Ready For Data : Active listener asserts this line to prevent data being put on the bus until it is ready for it.

• No Data Accepted  : An active listener asserts this line to indicate it has not yet accepted the last byte on the bus.

PIN OUT TABLE FOR IEEE 488