TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-18
V2.0, 2007-07
EBU, V2.0
13.3.6
Reaction to an PLMB Access to the External Bus
The reaction of the to a external bus request from an PLMB master is controlled as
shown in
Figure 13-8 EBU Reaction to PLMB to External Bus Access
If the EBU is operating in No Bus Mode, it is not possible for an PLMB master to access
the external bus. For this reason, the EBU generates an PLMB error whenever an
attempt is made to access the external bus while in No Bus Mode.
If the EBU is operating in Sole Master Mode, it has access to the external bus at all times
and as a result it is possible for the EBU to immediately perform the required external
bus access.
If the EBU is operating in Arbiter or Participant Modes and receives a request for an
external access from an PLMB or FPI bus master when it is not the owner of the external
bus (or is not able to retain ownership of the bus), the request is rejected with a “retry”.
MCA05719
PLMB Master generates
access to external bus
yes
no
Perform external bus
access
yes
Arbitration Mode =
"No Bus"?
Arbitration Mode =
"Sole Master"?
Reject PLMB access
with ERROR (external
bus is not available)
EBU has and
can retain ownership of the
external bus?
no
yes
no
Return acknowledge/
result to PLMB master
Reject PLMB access
with RETRY
Request ownership
of external bus
Done