IDT Bus Arbitration
Memory and Peripheral Bus Arbitration
79RC32438 User Reference Manual
5 - 14
November 4, 2002
Notes
Memory and Peripheral Bus Arbitration
The RC32438 allows external bus masters on the memory and peripheral bus. An external bus master
asserts the bus request (BRN) input to the RC32438 to request ownership of the memory and peripheral
bus.
1
The RC32438 responds to the assertion of BRN by relinquishing ownership of the memory and
peripheral bus by asserting bus grant (BGN) and simultaneously tri-stating
2
the following signals:
MADDR[25:0],
MDATA[15:0],
BWEN[1:0],
OEN,
RWN,
CSN[5:0],
BOEN,
BDIRN.
Read Value:
Previous value written
Write Effect:
Modify value
P2
Description:
Priority 2 Sneak Transaction Enable
. When this bit is set, the CPU may be granted access to
the PMBus during otherwise idle cycles while a priority 2 master is granted ownership of the
IPBus or ownership is pending to a priority 2 master.
Initial Value:
0x0
Read Value:
Previous value written
Write Effect:
Modify value
P3
Description:
Priority 3 Sneak Transaction Enable
. When this bit is set, the CPU may be granted access to
the PMBus during otherwise idle cycles while a priority 3 master is granted ownership of the
IPBus or ownership is pending to a priority 3 master.
Initial Value:
0x0
Read Value:
Previous value written
Write Effect:
Modify value
POI
Description:
Park On IPBus
. When the PMBus is idle, it is normally parked on the CPU. When the PMBus is
idle and this bit is set, the PMBus is parked on the IPBus.
Initial Value:
0x0
Read Value:
Previous value written
Write Effect:
Modify value
1.
Once an external bus master has requested the bus by asserting BRN, it must keep BRN asserted until it is
granted the bus (i.e., it observes BGN asserted).
2.
CSN[5:0] and BOEN shall have been in their negated state for at least one EXTCLK clock cycle before being tri-
stated. This is true when both the RC32438 or the external bus master relinquish ownership.