
PRS28.4G
IBM Packet Routing Switch
Programming Interface and Internal Registers
Page 50 of 131
prs28.03.fm
August 31, 2000
4.1.5 Operational Protocol
OCM Instruction operations are invoked when the EMB_MODE input is `0' and the EMB_SELECT input is `0'.
Data transferred over EMB_DATA_IN is shifted into the OCM instruction register. Serial data shifted in must
begin with the least significant bit of the instruction and end with the most significant bit of the instruction to be
executed. This scan operation is synchronized with the EMB CLOCK lines. Instructions always execute one
cycle after the EMB_SELECT changes from an active to an inactive state. “OCM Instruction Mode
Sequence,” table describes the sequence of events required to load and execute an OCM instruction.
When configured in a daisy chain (ring) structure, targeted OCMs (that is those with no instruction to execute)
must be loaded with NOOP instructions.
4.2 OCM Scan Mode
Note:
This mode is for system bring-up only.
4.2.1 Operational Protocol
Before a scan operation can occur, the system clock must be stopped and a scan string must be selected
using the OCM EVENT command. The clocks can be stopped and a scan string selected by issuing either
one or two EVENT instruction. Or, two separate EVENT instructions can be issued.
Scan operations are invoked when the EMB_MODE input is `1'b and the EMB_SELECT input is `0'b. Data
transferred over EMB_DATA_IN is serially shifted into the selected scan string. The logic values located
within the scan string are serially shifted out of the scan string over the EMB_DATA_OUT primary output.
One bit of data is shifted with each EMB A/B clock sequence.
The table below is a summary of the sequence of operations required to perform a scan write operation to an
OCM in a ring structure.
Table 15: OCM Instruction Mode Sequence
Controller Action
OCM Action/Response
Set EMB_MODE = 0; EMB_SELECT = 0 (Active)
Instruction/status operation specified
Serially shift instructions to all OCMs - NOOPs must be
loaded into all non-targeted OCMs
As instructions are serially shifted in through the EMB_DATA_IN pin.
The response word (that is, the results of the previous instruction) is
shifted out through the EMB_DATA_OUT pin.
Set EMB_SELECT = 1 (Inactive)
Instruction shifted mode is terminated and the currently load instruction
is executed. The contents of the OCM response register are instruction
dependent. Refer to “OCM Instruction Set definition” table for a
description of the individual instructions and a definition of the
response register contents following instruction execution.
Table 16: OCM Scan Mode Sequence
Controller Action
OCM Action/Response
Send EVENT instructions to all OCMs to stop system clocks (if
needed) and select one of two scan strings.
The OCMs will execute the EVENT instruction. The system clock
control command will be executed first, and then the selected
scan string will be placed between EMB_DATA_IN and
EMB_DATA_OUT.
Set EMB_MODE = 1; EMB_SELECT = 0 (Active).