
Chapter 12. Test
12-19
BIST
The ColdFire Version 4 reference design handles up to 64-Kbyte memory sizes, using the
memory size indicator to create a specific test for each memory. The cf4_core_kbus_tcu
provides global control of each BIST controller associated with each memory.
BIST memory controllers now have automatic hold logic. Two holds are performed during
the first background. The bisthold signal indicates when the memory is in a hold state; the
bistrelease input removes memories from the hold state.
12.3.2 BIST Core Ports
During memory array testing, BIST ports must be set as shown in Table 12-3. Memory
BIST logic has two modes chosen through mtmod[2:0]. Production BIST (PBIST)
indicates failing or passing devices. Engineering BIST (EBIST) characterizes memory. The
resetB signal is driven with an OR of MTMOD equal to the modes (see Table 12-3). The
remaining core signals are set to an inactive state. All signals are registered at the CF4e
boundary.
The bistdata output operates at half the processor clock frequency; all other BIST signals
operate at system clock speed. The system/processor clock ratio does not affect BIST
operation. If this were a pad-level rather than a core-level boundary, MTMOD would be
expanded from 2:0 to 3:0 where the assertion of MTMOD3 indicates PLL bypass mode,
and a hizb signal would be asserted during data retention to three-state the outputs.
Table 12-3. BIST Core Pins
Port Name
I/O
BIST Mode
Description
bistdone
Output
PBIST
Indicates the test is complete. The largest memory size determines cycle
run-time for production test. When asserted, bistdone remains asserted and
the PBIST stops. During BIST initialization, this signal toggles (0-1-0) for a
stuck-at fault test on this individual signal. Because bistdone is registered at
the core boundary, a few cycles are added to BIST run time for signal output
generation.
bistfail
Output
PBIST
Indicates a memory array failed. Once asserted, bistfail remains asserted
and PBIST stops. During BIST initialization, bistfail toggles from 0-1-0 for a
stuck-at-fault test.
bisthold
Output
PBIST/
EBIST
Indicates when BIST memory controllers are in a hold state. allowing the
user to begin timing data retention. During BIST initialization, bisthold
toggles from 0-1-0 for a stuck-at-fault test.
bistdata[3:0]
Output
EBIST
Outputs bit-map array data. Operates at 1/2 of the processor clock
frequency. Section 12.3.8, “Memory Data Retention,” gives cycle-by-cycle
details. For pad-level boundaries, bistdata can be muxed with pstddata[3:0].
mtmod[2:0]
Input
PBIST/
EBIST
During BIST, mtmod is applied one cycle before use.
101 PBIST mode. Asserted during the entire PBIST memory test.
110 EBIST mode. Asserted during the entire EBIST test, used to
characterize the array selected by bistmemory[2:0].
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.