12-18
ColdFire CF4e Core User’s Manual
For More Information On This Product,
Go to: www.freescale.com
BIST
Memory data retention
Timing
The Version 4 test methodology for testing memories differs from the Version 3 approach
in the following respects:
In Version 4, the BIST control logic is integrated into the memory controllers rather
than being a separate, added function. This solution supports all V4 memories sizes;
KRAM and KROM sizes from 512 bytes to 64 Kbytes and cache sizes from 2 to 32
Kbytes. This enhancement from the Version 3 BIST is developed around the
memories after memory size is selected for a design. In the Version 3 scheme,
modification of any memories requires rework of BIST logic.
Data retention methodology adds automatic hold logic to the BIST controllers,
which greatly simplifies control logic for data retention and reduces the knowledge
and intervention needed by the user/tester.
Simplifying data retention logic eliminates the need for staggering hold signals for
different size memory arrays. In Version 3, MTMOD signals controlled assertion
and release of the BIST hold signals for memory devices. Due to BIST hold
encodings, MTMOD signals had processor clock timing associated with them. In
Version 4, MTMOD signals have system clock timing associated with them because
hold logic is removed from the MTMOD decode. In addition, significantly fewer
modes are needed with MTMOD for BIST.
12.3.1 BIST Memory Controllers
Control logic includes BIST memory controllers for each memory, reducing critical timing
paths by collapsing sequential multiplexing of address lines. This reduces wiring and
simplifies register sharing. Figure 12-15 shows how this change embeds BIST logic in the
core.
Figure 12-15. CF4e BIST Hierarchy
Design containing the CF4e and memories
ICU
Data
ICU
Tag
OCU
Data
OCU
Tag
RAM
0
RAM
1
ROM
0
ROM
1
CF4e Core
cf4_core_kbus_tcu
Core
ICU
Data
and
BIST
Control
ICU
Tag
and
BIST
Control
OCU
Data
and
BIST
Control
OCU
Tag
and
BIST
Control
RAM
0
and
BIST
Control
RAM
1
and
BIST
Control
ROM
0
and
BIST
Control
ROM
1
and
BIST
Control
F
Freescale Semiconductor, Inc.
n
.