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SCAN18373T
Description of Boundary-Scan Circuitry
The scan cells used in the BOUNDARY-SCAN register are
one of the following two types depending upon their loca-
tion. Scan cell TYPE1 is intended to solely observe system
data, while TYPE2 has the additional ability to control sys-
tem data.
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 acti-
vate 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.
Bypass Register Scan Chain Definition Logic 0
The INSTRUCTION register is an eight-bit register which
captures the value 00111101.
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 SCAN18373T device. SCAN CMOS Test Access
Logic devices do not include 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.
Instruction Register Scan Chain Definition
MSB
→ LSB
Scan Cell TYPE1
Scan Cell TYPE2
Instruction Code Instruction
00000000 EXTEST
10000001 SAMPLE/PRELOAD
10000010 CLAMP
00000011 HIGHZ
All Others BYPASS
