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technical note
A G R E A T E R M E A S U R E O F C O N F I D E N C E
Creating External
Instrument Drivers for
the Model 4200-SCS
Introduction
As the measurements performed on semiconductor devices grow increas-
ingly complex, so does the demand for measurement automation. A
typical test setup often involves several instruments performing sourcing,
measurement, or auxiliary functions, all connected to a common commu-
nications bus (typically GPIB) and controlled by a PC station. The Model
4200-SCS parameter analyzer eliminated the need for a dedicated PC. The
Keithley Interactive Test Environment (KITE) allows the Model 4200-SCS
to perform as both a parameter analyzer and an external instrument con-
troller, making it the "command-and-control center" of the entire instru-
ment rack. KITE software already supports several popular instruments,
such as pulse generators, switch matrices, and C-V analyzers, through
software control modules known as drivers.
Occasionally, a user may need to control an instrument that's not sup-
ported by a standard Keithley driver library. This technical note describes
how to create custom instrument drivers. It assumes the reader is already
familiar with the basic operation and software environment of the Model
4200-SCS, as well as with programming in C language.
Overview
In general, the Model 4200-SCS can control any external instrument
connected to either the IEEE-488 (GPIB) bus or the RS-232 (serial) com-
munication port, thanks to its flexible PC-based architecture. The GPIB
protocol is currently the most widely used one. Figure 1 illustrates a
multi-instrument system configuration.
In the Model 4200-SCS, external equipment is controlled via the User
Test Modules (UTMs), which are essentially C functions created and main-
tained with the Keithley User Library Tool (KULT). Figure 2 illustrates the
relationship between user modules, user libraries, UTMs, KITE, and KULT.
From an operator's perspective, controlling an external instrument via a
UTM is very similar to programming that instrument from its own front
panel. Once all the instrument settings are entered and saved, running
an instrument is as easy as clicking the Run button in KITE. The added
advantage of external control, however, is that now this UTM can be in-
corporated into a larger KITE project and become a part of a 4200-based
automated test setup. Data collection, processing, graphing, and storage
are also simplified.
technical note
Creating External Instrument Drivers
for the 4200-SCS
Figure 1.
Figure 2.
technical note
Driver Structure
An instrument driver can be as simple or as complex as the function the Initialize/Clear/Reset
instrument is asked to perform. Typically, external instruments fall into Measurement
Instrument
two general categories: auxiliary devices (e.g., wafer probers, thermal
chuck controllers, pulse generators, switch mainframes) and measure-
ment instruments (e.g., C-V meters, LCR meters, oscilloscopes). Perform Function
(e.g., Move Chuck
Auxiliary device drivers are typically structured as illustrated in Figure 3. or Close Relay)
Note that the auxiliary devices require mostly one-way communication
from the controller, which makes the drivers very simple. Measurement Return
instruments perform more complex functions; therefore, their drivers are Status/Feedback
(optional)
usually more complex. A typical measurement instrument driver is struc-
tured as illustrated in see Figure 4.
General Considerations Done
Let's look at an example from the standard Keithley libraries (the existing
libraries that come standard on every Model 4200-SCS). Figure 3.
The standard library for semi-automatic probers on the Model 4200-SCS
is called PrbGen (for Prober Generic). This library contains four modules:
Initialize/Clear/Reset
PrInit (Prober Initialize), PrChuck (Prober Chuck), PrMovNxt (Prober Measurement
Move Next), and PrSSMovNxt (Prober SubSite Move Next). Without getting Instrument
into the details of implementation of these modules, it's easy to see this
library addresses three primary functions of a semi-automatic prober:
Set Up Instrument