Datasheet

Section 6 Bus Controller (BSC)
Rev. 3.00 Mar 17, 2006 page 257 of 926
REJ09B0283-0300
temporary release of the bus in the event of an external access request from an internal bus master.
For details see section 8, EXDMA Controller.
External Bus Release: When the BREQ pin goes low and an external bus release request is issued
while the BRLE bit is set to 1 in BCR, a bus request is sent to the bus arbiter.
External bus release can be performed on completion of an external bus cycle.
6.13 Bus Controller Operation in Reset
In a reset, this LSI, including the bus controller, enters the reset state immediately, and any
executing bus cycle is aborted.
6.14 Usage Notes
6.14.1 External Bus Release Function and All-Module-Clocks-Stopped Mode
In this LSI, if the ACSE bit is set to 1 in MSTPCR, and then a SLEEP instruction is executed with
the setting for all peripheral module clocks to be stopped (MSTPCR = H'FFFF) or for operation of
the 8-bit timer module alone (MSTPCR = H'FFFE), and a transition is made to the sleep state, the
all-module-clocks-stopped mode is entered in which the clock is also stopped for the bus
controller and I/O ports. In this state, the external bus release function is halted. To use the
external bus release function in sleep mode, the ACSE bit in MSTPCR must be cleared to 0.
Conversely, if a SLEEP instruction to place the chip in all-module-clocks-stopped mode is
executed in the external bus released state, the transition to all-module-clocks-stopped mode is
deferred and performed until after the bus is recovered.
6.14.2 External Bus Release Function and Software Standby
In this LSI, internal bus master operation does not stop even while the bus is released, as long as
the program is running in on-chip ROM, etc., and no external access occurs. If a SLEEP
instruction to place the chip in software standby mode is executed while the external bus is
released, the transition to software standby mode is deferred and performed after the bus is
recovered.
Also, since clock oscillation halts in software standby mode, if BREQ goes low in this mode,
indicating an external bus release request, the request cannot be answered until the chip has
recovered from the software standby state.