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MBIST Instruction Register
ARM DDI 0414C
Copyright © 2008 ARM Limited. All rights reserved.
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3.2.2
Control field, MBIR[51:46]
This 6-bit control field specifies the MBIST function. Table 3-3 shows how the five LSB
bits of the Control field affect the behavior of the MBIST controller.
MBIR[51]
selects a nonsticky or sticky fail flag,
MBISTRESULT[1]
:
•
When
MBIR[51]
is set, the fail bit toggles in real time. It goes HIGH for failing
comparisons and LOW for passing comparisons.
Note
Setting
MBIR[51]
can cause the fail bit to toggle at the test frequency. It is not
recommended when the external pin or the ATE cannot follow the test frequency.
•
When
MBIR[51]
is cleared, the fail bit is sticky. It remains HIGH after the first
failure until a new MBIST instruction shifts in or until the data log shifts out.
3.2.3
Read Latency and Write Latency fields, MBIR[42:40] and MBIR[45:43]
The Read Latency and Write Latency fields of the MBIR are used to specify the read
and write latency of the RAM under test. Read and write latencies are the numbers of
cycles that the RAM requires to complete read and write operations. For example, in a
write to a RAM with a write latency of two cycles, the RAM inputs are valid for a single
cycle. The next cycle is a NOP cycle with the chip enable negated. Similarly, in a read
from a RAM with a read latency of three cycles, the RAM inputs are valid for a single
cycle. After two NOP cycles, the read data is valid on the RAM outputs.
Note
Even if the RAM under test uses the same latency for both read and write operations,
you must still program both the read latency and write latency fields of the MBIR with
the same value.
Table 3-3 Control field encoding (five LSB bits)
Control MBIR[50:46]
Behavior
Description
bx00000
Default
Test runs to completion. If
MBIR[51]
is 0, sticky fail present after first
failure.
bx00001
Stop-on-fail
End of test on failure.
bx00011
Bitmap mode
Enables logging of each failure. See