STS 1000 Unleashed

A leviathan monster has been the butt of many a joke cracked on the first floor. It is downright ugly, does not fit in the interior decor and sucks in all the cool air the airconditioner has to offer! In this age, where COM is the guiding light and distributed processing the order of the day, it is a throwback to the old primitive days of computing, with a central repository having a mere 50MB of memory, and a program size limitation of 32KB!!

All it’s utilities communicate on the old and trusted IEEE-488 HPIB bus, under the control of an A-600 processor(ever heard of it? ) . Yet, the group swears by it. No effort to keep it up and running is too great for them, no jokes good enough to test their patience! To them, STS 1000 is more than a means of bread &butter, it’s a religion, a way of life. A peep into this amazing paradox throws to light some interesting facts. Ever heard of a Real Time OS which controls as many as 63 instruments? Which can run six different user sessions? Which is a multiprogramming OS? Well, if your thought process centered on QNX, I wouldn’t blame you. But it’s not QNX I’m talking about, it’s a relatively unknown, but highly rugged Operating System HP’s RTE-A, which takes the credit for this seemingly impossible task. That’s not all. What would you do if the utilities on this Operating System became obsolete and you have absolutely no documentation for the same? Don’t say that you’d buy a new system because that means investing something close to $600,000. And don’t say that you can do without it because that means that means you’d be putting your Avionics module into the aircraft without it having been tested on the ground!!

So, finally exasperated you’d turn to the only possible answer, the one the STS 1000 team has to offer, one of emulating the utilities. For instance, replace the HP-1000’s touch sensitive screen, which is linked to the host over a COM port (before I forget, it’s not the COM of Microsoft Usage, it’s a communications port), with a PC and emulate the entire touch screen to the PC monitor. And that’s just what they did! A full fledged Terminal Emulation software for the HP-150A touch screen terminal was developed in a time frame of just six months! A peep into this wonderful world of ATE and the STS 1000 is given below by this bunch of die-hard optimists. On their shoulders rest the hopes of many an airline companies who want their STS 1000 stations to see the turn of the century---without them getting obsolete.

The STS Team Mani, Das, Narayana and Thantry (left to right) with the STS 1000. The other members are Shamal and Jaya

AUTOMATIC TEST EQUIPMENT (ATE)

What is ATE ?

Automated test equipment which is popularly known as ATE is Equipment designed to test the electronic components, modules, systems with the aid of a Computer as a controller.

Classification of ATE’s:

ATE’s can be broadly classified based on their use.

1. Component ATE’s: These ATE’s are basically used to test the electronic components for their specifications. They range from resistor checking to complex microchip testing ATE’s. Leading ATE manufacturers in this area are Terradyne, Dynapart etc.

2. Assembled PCB or Board Testing ATE’s: These are the type of ATE’s basically used to test the assembled component’s PCB’s. These types of ATE’s generally makes use of ‘Bed-Of-Nail’ fixtures for mounting the board or unit under test (UUT). They carry out tests by accessing each nodal point on the PCB where components are mounted. Schlumberger, Genrad, Terradyne, HP are few leading manufacturers of these type of ATE’s.

These ATE’s carry out two types of tests on UUTs. Firstly they check the circuit layout correctness and then checks each component for its goodness. Since components are mounted (assembled) on the PCBs,the checking of each component requires electrical isolation from rest of circuitry. The tester achieves it through floating ground technique. Each component in the board is tested for its specification and microchips are also tested in the same way for its internal logic. This way the entire populated board is tested . This type of test is popularly known as "IN-CIRCUIT TEST". The second type of test called "FUNCTIONAL TEST" involves testing the UUT for its end specifications.

The recent advancements in the PCB technology with the advent of SMT the ‘surface mount technology (SMT)’ which do not have plated through holes have brought lot of difficulty in testing the Boards. The recent testers have a new technology called the "Boundary Scan Testing (BST)" in which components mainly IC’s and complex Microchips are checked for their goodness after their assembly on the PCB.

3. Unit or System level ATE’s: The typical architecture of this type of Tester is a Rack & Stack instrumentation with computer as a controller connected by means of a parallel communication bus called General Purpose Interface Bus (GPIB) with its protocol. The controller controls the switching of the signal between different Instruments connected through the Bus and thereby the UUT to be tested is given specified signal level and monitored for its desired output signal.

GENERAL PURPOSE INTERFACE BUS:

HP designed this protocol to connect their line of programmable instruments to the computers for remotely controlling them. GPIB devices communicate with other GPIB compatible devices (or instruments) by sending device dependent messages and interface messages through the interface system.

The device dependent messages are called data messages. These contain messages specific to a particular instrument such as programming instructions, measurement results etc. Interface messages manage the bus usually called command messages such as initializing the bus, addressing and unaddressing the devices etc.

GPIB devices can be talkers, listeners or controllers. The controller who is typically the computer, manages the GPIB bus for the flow of information by sending commands to all devices. A device or instrument can take up the role of talker or listener. A talker sends data to one or more listeners, which receives the data. For example, the voltmeter, an instrument for measuring the voltages, current, resistance is the talker where as a printer who receives the data is called the listener.

The GPIB bus is like an ordinary computer bus except that the standard cables are used to inter connects the devices. The role of computer can be thought of as a switching center which monitors the communication network (GPIB).When the center (controller) notices that a party(device) wants to make a call (send a data message), it connects the caller(talker) to the receiver(listener).

Here each device in the controller has a unique GPIB address and the controller makes use of this address to enable the specific instruments. The communication starts with the controller addressing the talker who wants to send messages and then he addresses the listener. Then a talker can send message to a receiver.

The UUT is connected to the Tester at its End connector and in many case the interface between the UUT and Tester is through a Fixture called Test Unit Adapter.

The recent development in these kinds of ATEs are use of a special kind of communication interface called VXI bus. Here the instruments and controller are all minitiarised into PCB or cards and these are controlled by VXI bus. Thus the size of ATE’s have come down drastically and the speed of the operation has increased significantly.

Now that you’ve the basic background of what an ATE is and what it does, it’s time you graduated to STS 1000. The STS-1000 is a system level ATE which consists entirely of instruments which are used for testing Line Replaceable Units (LRU’s) which ultimately go to the aircraft cockpit. A couple of well known LRU’s are the Mode Control Panel(MCP), the Flight Control Computer(FCC) and the Advanced Flight Manager Computer(AFMC), all of which can be tested on the STS 1000 Test station. The test cases, technically called the Test Program Sets (TPS) for these LRU’s are written in the ATLAS programming language which looks a bit like COBOL !

The STS-1000 is modular in design, instruments on the station can be replaced with little modification in the driver software and is controlled by a robust HP-1000 controller, which has the Real Time OS, RTE-A running on it.

The test bed for running the TPS is the elegant Honeywell Proprietary application, the Test Executive. It manages the resources on the HP-1000, acts as an interface between the Operating System and the Application(the TPS) and provides a user interface to the unskilled operator.

So, the next time the airconditioner doesn’t give you the cool air you expect, don’t fret or fume. Instead, think of the numerous test cases that the STS-1000 test station might be running, just to ensure that you get an accident free passage the next time you travel by air.

STS 1000 Team (contributed by Narayana, Thantry and Mani)