TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-11
V2.0, 2007-07
EBU, V2.0
Figure 13-4 Arbitration Sequence with the EBU in Arbiter Mode
In Arbiter Mode, the arbitration sequence starts with the EBU as owner of the external
bus.
Table 13-6
Function of Arbitration Pins in Arbiter Mode
Pin
Type Pin Function in Arbiter Mode
HOLD
In
In Owner Mode (EBU is the owner of the external bus), a low level at
HOLD indicates a request for bus ownership from the external
master.
In Hold Mode (EBU is not the owner of the external bus), a high level
at HOLD indicates that the external master has relinquished bus
ownership, which causes the EBU to exit Hold Mode.
HLDA
Out
While HLDA is high, the EBU is operating in Owner Mode. A high-to-
low transition indicates that the EBU has entered Hold Mode and that
the external bus is available to the external master.
While HLDA is low, the EBU is operating in Hold Mode. A low-to-high
transition indicates that the EBU has exited Hold Mode, and has
retaken ownership of the external bus.
BREQ
Out
BREQ is high during normal operation. The EBU drives BREQ low
for two EBU clock cycles after entering Hold Mode (after asserting
HLDA low).
BREQ returns high one clock cycle after the EBU has exited Hold
Mode (after driving HLDA high).
HLDA
(EBU Output)
EBU on Bus
MCT05715
HOLD
(EBU Input)
1)
4)
2)
5)
3)
6)
2 Cycles
BREQ
(EBU Output)
External Bus
External Master on Bus
EBU on Bus
≥
1 Cycle
1 Cycle
