NSC SCAN18540TMDA Datasheet
SCAN18540T
Inverting Line Driver with TRI-STATE
®
Outputs
General Description
The SCAN18540T is a high speed, low-power line driver featuring separate data inputs organized into dual 9-bit bytes
with byte-oriented paired output enable control signals. This
device is compliant with IEEE 1149.1 Standard Test Access
Port and Boundary Scan Architecture with the incorporation
of the defined boundary-scan test logic and test access port
consisting of Test Data Input (TDI), Test Data Out (TDO),
Test Mode Select (TMS), and Test Clock (TCK).
Features
n IEEE 1149.1 (JTAG) compliant
n Dual output enable signals per byte
n TRI-STATE outputs for bus-oriented applications
n 9-bit data busses for parity applications
n Reduced-swing outputs source 24 mA/sink 48 mA (Mil)
n Guaranteed to drive 50Ω transmission line to TTL input
levels of 0.8V and 2.0V
n TTL compatible inputs
n 25 mil pitch Cerpack packaging
n Includes CLAMP and HIGHZ instructions
n Standard Microcircuit Drawing (SMD) 5962-9312701
Connection Diagram
Pin Names Description
AI
(0–8)
Input pins, A side
BI
(0–8)
Input pins, B side
Pin Names Description
AOE
1
, AOE2TRI-STATE Output Enable Input pins,
A side
BOE
1
, BOE2TRI-STATE Output Enable Input pins,
B side
AO
(0–8)
Output pins, A side
BO
(0–8)
Output pins, B side
TRI-STATE®is a registered trademarkof National Semiconductor Corporation.
DS100323-1
September 1998
SCAN18540T Inverting Line Driver with TRI-STATE Outputs
© 1998 National Semiconductor Corporation DS100323 www.national.com
Truth Tables
Inputs AO (0–8)
AOE
1
AOE
2
AI (0–8)
LL H L
HX X Z
XH X Z
LL L H
Inputs BO (0–8)
BOE
1
BOE
2
BI (0–8)
LL H L
HX X Z
XH X Z
LL L H
H
=
HIGH Voltage Level
X=Immaterial
L=LOW Voltage Level
Z=High Impedance
Block Diagrams
Byte-A
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Tap Controller
DS100323-3
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Block Diagrams (Continued)
Byte-B
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Note: BSR stands for Boundary Scan Register
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Description of BOUNDARY-SCAN Circuitry
The scan cells used in the BOUNDARY-SCAN register are
one of the following two types depending upon their location.
Scan cell TYPE1 is intended to solely observe system data,
while TYPE2 has the additional ability to control system
data. (See IEEE Standard 1149.1
Figure 10–11
for a further
description of scan cell TYPE1 and
Figure 10–12
for a fur-
ther description of scan cell TYPE2.)
Scan cell TYPE1 is located on each system input pin while
scan cell TYPE2 is located at each system output pin as well
as at each of the two internal active-high output enable signals. AOE controls the activity of the A-outputs while BOE
controls the activity of the B-outputs. Each will activate their
respective outputs by loading a logic high.
The BYPASS register is a single bit shift register stage identical to scan cell TYPE1. It captures a fixed logic low.
The INSTRUCTION register is an 8-bit register which captures the default value of 01001101.The two least significant
bits of this captured value (01) are required by IEEE Std
1149.1. The upper six bits are unique to the SCAN18540T
device. SCAN CMOS Test Access Logic devices do not in-
clude the IEEE 1149.1 optional identification register. Therefore, this unique captured value can be used as a “pseudo
ID” code to confirm that the correct device is placed in the
appropriate location in the boundary scan chain.
MSB→LSB
Instruction Code Instruction
00000000 EXTEST
10000001 SAMPLE/PRELOAD
10000010 CLAMP
00000011 HIGH-Z
All Others BYPASS
Bypass Register Scan Chain Definition
Logic 0
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Instruction Register Scan Chain Definition
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Description of BOUNDARY-SCAN Circuitry (Continued)
Scan Cell TYPE1
DS100323-7
Scan Cell TYPE2
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