S1X60000 Datasheet, PDF (250/358 Pages) Epson Company – EMBEDDED ARRAY

Chapter 10 Circuit Design that Takes Testability into Account
10.5 Memory BIST Design
The S1X60000 series comes equipped with a memory self diagnostic circuit called the
“Memory BIST (Built In Self Test),” which may be used as a test circuit for testing the LSI’s
internal memory. Use of the memory BIST provides numerous advantages, including those
specified below.
• Eliminates the need for customers to design a memory test circuit
• Allows the number of external pins for memory testing to be reduced
• Capable of testing memory at an actual high operating speed
• Allows the time required for memory testing using an LST tester to be reduced
In addition, it offers versatile optional functions such as a bypass circuit (transparent
circuit) for memory inputs, as a means of increasing fault detection rates for the entire
chip.^*1
Note
*1: If fault detection rates are to be increased, the LSI must be modified so as to be
suitable for SCAN testing following the insertion of a bypass circuit. If it is
necessary to make the entire chip suitable for SCAN testing, a bypass circuit
must also be optionally included in the memory BIST.
10.5.1 Outline of the Memory BIST Circuit Block
The memory BIST generates a circuit known as a “collar” in the periphery of the memory,
and a circuit known as a “controller” that controls the collar. If multiple pieces of memory
are included, multiple collars are generated that can be controlled by a single controller (for
purposes of overhead reduction).
In addition, a bypass circuit or a fault diagnosis function may be added to inputs for
memory as necessary. Under no circumstances can the number of elements inserted for
memory inputs exceed the number of multiplexer stages, however. When the memory BIST
is inserted, a circuit block becomes similar to that depicted in Figure 10-10, and a bypass
circuit becomes similar to that depicted in Figure 10-11 (in both, memory BIST design is
applied to synchronous type RAM).
EMBEDDED ARRAY S1X60000 SERIES
DESIGN GUIDE
EPSON
241