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PDF EB203 Data sheet ( Hoja de datos )
| Número de pieza | EB203 | |
| Descripción | Test Bus Controller | |
| Fabricantes | ETC | |
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EB203
Test Bus Controller
SN74ACT8990
Author Peter Forstner
Date: 01.07.92
Rev.: 1.0
1 page  
TEXAS INSTRUMENTS
Introduction
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1. Introduction
There has been a dramatic increase in the complexity of electronic systems,
as a result of advances in the integration of semiconductors, the introduction
of new packaging techniques (SMD), and the consequent use of double-
sided circuit boards. However, increased component density on circuit
boards brings with it new problems of testability, since the number of the
necessary test vectors increases out of proportion with complexity. By
making use of nail bed adapters, it is possible to partition the system to be
tested, and so to reduce significantly the number of test vectors, although
high SMD component density on double-sided boards reduces the number of
possible contact areas for nail bed adapters. The escalating problems of
testability can therefore only be solved with a completely new concept.
Back in 1985, leading electronic manufacturers founded the Joint Test
Action Group (JTAG), in order to develop a new and cost-effective test
concept. The result of this was the IEEE 1149.1 standard. This standard
requires the use of special test-circuits at the inputs and outputs of selected
semiconductor components, together with logic to control such test-circuits.
A 4-wire serial test bus combines the test-circuits into a complete test-group,
which is controlled via the test bus; in this way, with only 4 lines the
complete system can be partitioned and tested.
The Texas Instruments(TI) Application Report EB193 describes these test
methods in detail, and presents the IEEE 1149.1-compatible SCOPE™ bus
drivers from TI. This Application Report EB203 assumes an understanding of
test-methods according to IEEE 1149.1
The control of an IEEE 1149.1-compatible test system is usually performed
by a computer. The TEST BUS CONTROLLER (TBC) SN74ACT8990 from
Texas Instruments can be connected to a computer like a normal interface
circuit, and it then controls completely the IEEE 1149.1 test bus.(Figure 1).
The computer first configures the TBC, and then loads in parallel the test
commands and test vectors. The TBC transfers these commands and
vectors to the system, and thereby generates the signal sequence required
by IEEE 1149.1. The processor can read the result in parallel from the TBC,
after the test data has addressed the logic to be tested. This Application
Report describes the operation of the TBC, and explains the programming
procedure with examples.
EB203
5
5 Page 
TEXAS INSTRUMENTS
Hardware
otherwise in a high impedance state. If the test bus signals must be buffered
(Figure 8), the TDO output of the test system can no longer be in a high
impedance state. For this eventuality, two test data inputs (TDI0, TDI1) are
available.
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Figure 6: Connection of an IEEE 1149.1 Test Bus to the TBC
Figure 7: Connection of Two IEEE 1149.1 Test Busses to the TBC
EB203
11
11 Page | ||
| Páginas | Total 70 Páginas | |
| PDF Descargar | [ Datasheet EB203.PDF ] | |
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