IBM 3745 Series, Hardware Maintenance Reference

Page: 635 / 712

Internal Interconnections
Internal Interconnections
As shown in “ESS Data Flow” on page 12-8, each ELA interconnects with the com-
munication subsystem (CSS) and the MOSS via the IOC bus and the DMA bus.
CSP-to-IOC Bus
This connection is used for:
Ÿ Communication with the NCP (through the same IOH high level commands as
the other HSS scanners)
Ÿ MOSS command exchange
Ÿ
ELA IML
Ÿ Diagnostics.
The physical interconnection between the ELA CSP and the CCU is identical to that
between the LSS CSP to the CCU (refer to Chapter 4, "Transmission Subsystem").
For board and card locations, see the Maintenance Information Procedures Manual.
NCP-ELA Microcode
The CCU uses IOH and IOHI to exchange data, commands and statuses with the
ELA CSP in the same way as with the LSS, but cycle steal is not used when the
EAC is running.
EAC to CSP
The physical interconnection between the EAC and the CSP is identical to that
between the FESH and the CSP of the HSS.
For board and card locations, see Maintenance Information Procedures Manual.
Microcode to EAC
The picocode is loaded from the CSP in each layer of the EAC RAM at IML time.
The EAC-to-CSP interconnection is activated and controlled via external registers
and control words (CW).
A CW is built by the CSP microcode and specifies the actions to be performed by
the EAC.
The CW is cycle stolen by EAC, then executed.
The EAC informs the CSP microcode when the action is completed.
EAC to DMA Bus
This connection is used for direct CCU storage access and specifically:
Ÿ NCP buffer prefix exchange
Ÿ Data transfer between the Ethernet LAN and main storage
The physical interconnection between the EAC and the DMSW is identical to that
between the FESH and the DMSW of the HSS.
Chapter 12. Ethernet Subsystem (ESS)
12-13