
MBIST Instruction Register
ARM DDI 0402B
Copyright © 2007, 2008 ARM Limited. All rights reserved.
3-7
3.2.2
Control field, MBIR[54:49]
The control field specifies the MBIST function. Table 3-3 shows how the control field
affects the behavior of the MBIST controller.
MBIR[54] selects a nonsticky or sticky fail flag,
MBISTRESULT[1]
:
•
When MBIR[54] is set, the fail bit toggles in real time. It goes HIGH for failing
comparisons and LOW for passing comparisons.
Note
Setting MBIR[54] 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[54] 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[44:41] and MBIR[48:45]
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
Control
MBIR[54:49]
Behavior
Description
bx00000
Default
Test runs to completion. If MBIR[54] = 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
Содержание PL310
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Страница 22: ...Introduction 1 8 Copyright 2007 2008 ARM Limited All rights reserved ARM DDI 0402B ...
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