TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-15
V2.0, 2007-07
EBU, V2.0
Figure 13-6 Arbitration Sequence with the EBU in Participant Mode
In Participant Mode, the arbitration sequence starts with the EBU in Hold Mode.
1. The EBU detects that it has to perform an external bus access by asserting a low
signal on the BREQ output.
2. When the external master is able to release bus ownership, the external master
releases the external bus by tri-stating its bus interface lines and drives the
HLDA = 0.
3. At least one clock (LMBCLK) cycle after issuing HLDA = 0, the EBU will start to drive
the external bus.
4. When the EBU is in Owner Mode, the external master may optionally drive HOLD = 0
to signal that it wants to regain ownership of the external bus.
5. When the criterias are met for the EBU to release the bus ownership, the EBU enters
Hold Mode and drives BREQ = 1 output high to signal that it has released the bus.
6. When the external master detects that the EBU has released the bus (BREQ = 1), it
returns HLDA to high level and takes ownership of the external bus.
7. The EBU will not request ownership of the external bus again (BREQ = 0) at least
one clock (LMBCLK) cycle after HLDA has been driven high).
8. In Owner Mode, the EBU will not request ownership of the external bus BREQ = 0)
for at least one clock (LMBCLK) cycle after its HOLD input has been driven high.
The conditions that cause change of bus ownership when the EBU is operating in
Participant Mode is shown in
HLDA
(EBU Output)
Ext. Master on Bus
MCT05717
BREQ
(EBU Output)
1)
5)
2)
6)
4)
HOLD
(EBU Input)
External Bus
EBU on Bus
Ext. Master on Bus
≥
1 Cycle
≥
1 Cycle
7)
≥
1 Cycle
8)
3)
