Vitrek V4 - Page 30

Vitrek V4 – Electrical Safety Tester USER MANUAL
29
syntax has been adopted by SCPI to provide common commands for the identical functions of different
programmable instruments.
Relationship between IEEE-488.1, IEEE-488.2, and SCPI
As shown in the figure 3, the IEEE-488.1 standard locates at layer A, the layer A belongs to the protocol of
interface function on the GPIB bus. The source handshake (SH), acceptor handshake (AH) and talker are
included to this layer (10 interface functions totally).
At layer B, the syntax and data structure could be the essence of entire IEEE-488.2 standard. The syntax
defines the function of message communication, which contain the <PROGRAM MESSAGE> (or simply
“commands”) and <RESPONSE MESSAGE>. The two kinds of messages represent the syntax formation of
device command and return value. The data structure is the constitution of status reporting, which
IEEE-488.2 standard have been defined.
The common commands and queries are included to layer C. Commands and queries can be divided into two
parts: mandatory and optional. Commands modify control settings or tell the instrument to perform a specific
action. Queries cause the instrument to send data or status information back to the computer. A question mark
at the end of a command identifies it as a query.
Layer D is interrelated with device information. Different devices have different functions. SCPI command
sets belong to this layer.
Command Syntax
If you want to transfer any instructions to an instrument, and comply with SCPI, there are three basic
elements must be included.
z Command header
z Parameter (if required)
z Message terminator or separator
Command Header
The command header has a hierarchical structure that can be represented by a command tree (Figure 4).
The top level of the tree is the root level. A root node is located at the root level. A root node and one or more
lower-level nodes form a header path to the last node called the leaf node.
SCPI
IEEE-488.2 IEEE-488.2
SCPIIEEE-488.1
AABBCCDD
Interface Function
Syntax & Status Data Structure
Common Command & Queries
SCPI
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 - TestEquipmentDepot.com