HP 8753E manual Data lines carry device-dependent instructions or data, SRQ Service Request

ATN (Attention)	The active controller uses this line to define whether
	the information on the data bus is command-oriented or
	data-oriented. When this line is true (low), the bus is in the
	command mode, and the data lines carry bus commands. When
	this line is false (high), the bus is in the data mode, and the
	data lines carry device-dependent instructions or data.
SRQ (Service Request)	This line is set true (low) when a device requests service
	and the active controller services the requesting device. The
	network analyzer can be enabled to pull the SRQ line for a
	variety of reasons such as requesting control of the interface,
	for the purposes of printing, plotting, or accessing a disk.
REN (Remote Enable)	This line is used exclusively by the system controller. When this
	line is set true (low), the bus is in the remote mode, and devices
	are addressed by the controller to either listen or talk. When
	the bus is in remote mode and a device is addressed, it receives
	instructions from the system controller via HP-IB rather than
	from its front panel (pressing ILocal) returns the device to
	front-panel operation). When this line is set false (high), the
	bus and ail of the connected devices return to local operation.
EOI (End or Identify)	This line is used by a talker to indicate the last data byte in a
	multiple-byte transmission, or by an active controller to initiate
	a parallel-poll sequence. The analyzer recognizes the EOI line
	as a terminator, and it pulls the EOI line with the last byte of a
	message output (data, markers, plots, prin% error messages).
	The analyzer does not respond to parallel poll.

HP-IB Requirements

Number of Interconnected Devices:15 maximum.

Interconnection Path Maxims Cable Length: 20 meters maximum or 2 meters per device

	(whichever is less).
Message Transfer Scheme:	Byte serial, bit parallel a synchronous data
	transfer using a 3-line handshake system.

Data Rate:

Address Capability:

Multiple-Controller Capability:

Maximum of 1 megabyte-per-second over the specified distances with t&state drivers. Actual data rate depends on the transfer rate of the slowest device connected to the bus

Primary addresses: 31 talk, 31 listen. A maximum of 1 talker and 14 listeners can be connected to the interface at given time.

In systems with more than one controller (like this instrument), only one controller can be active at any given time. The active controller can pass control to another controller, but only the system controller can assume unconditional control. Only one system controller is allowed.

11-16 Compatible Peripherals