參數(shù)資料
型號： IBM32NPR100EXXCAB133
英文描述： Microprocessor
中文描述： 微處理器
文件頁數(shù)： 51/131頁
文件大?。?/td> 1679K
代理商： IBM32NPR100EXXCAB133
PRS28.4G
IBM Packet Routing Switch
prs28.03.fm
August 31, 2000
Programming Interface and Internal Registers
Page 51 of 131
4.2.2 Scan String Access from OCM
The scan chain that is accessible via the OCM is all internal latches, except the boundary latches. The
boundary latch scan chain is only accessible via the JTAG interface. Also, the bypass latch is selectable for
OCM scan mode.
The Internal Scan String is used to access the internal latches (including GRAs) except the Boundary latches,
the OCM logic block latches, the IEEE 1149.1 logic block latches, and the Clock, BIST, Reset logic block
latches.
The Bypass Scan String contains a single bit latch. This scan string is selected when multiple PRS28.4G
devices are connected in a “ring-bus” configuration. By selecting the Bypass Scan String, scan data can
move quickly to another PRS28.4G device.
4.3 Built In Self Test (BIST)
The Built In Self Test (BIST) function is a means of testing the internal logic of the device via the OCM. BIST
is initiated by issuing an OCM EVENT command.
BIST is accomplished with a BIST state machine which interfaces with the Pseudo-Random Pattern Gener-
ator (PRPG), the Multiple Input Signature Register (MISR), clock control logic, and the flush reset function.
4.3.1 Pseudo-Random Pattern Generator (PRPG)
The on-chip PRPG is based on a Linear Feedback Shift Register which has a characteristic length of 32 bits.
This size was chosen to support up to sixteen scan chains where each scan chain was subdivided into two
separate chains during BIST. This subdividing of scan chains reduces the total length of the chain and hence
the scan time required to load and unload the random patterns during the BIST operation. The characteristic
polynomial implemented in the PRS28.4G PRPG:
4.3.2 Multiple Input Signature Register (MISR)
Like the PRPG, the MISR is based on a Linear Feedback Shift register with the characteristic length of 32.
The characteristic polynomial is identical to that used in the PRPG. It also is implemented using scan-only
latches and XOR logic to generate the feedback terms. Each MISR bit input, scan chain output, is XORed
with the previous bit of the MISR to produce a compressed MISR value.
Write scan data to OCMs. One bit of scan data must be sent for
each latch in the selected scan chains.
OCMs receive data from EMB_DATA_IN which is shifted into
the selected scan string. Old scan data shifts out of the
EMB_DATA_OUT.
Set EMB_SELECT = 1 (Inactive).
Scan operation ends. Targeted OCM maintains EVENT instruc-
tion in the instruction register.
Table 16: OCM Scan Mode Sequence
Controller Action
OCM Action/Response
X
32
X
31
X
30
X
10
1
+
+
+
+
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