SH7712 Datasheet, PDF (498/978 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 12 Bus State Controller (BSC)
while the SDRAM waits for the refresh. The LSI asserts the REFOUT pin until the bus mastership
is received. If the slave releases the bus, the LSI acquires the bus mastership to execute the
SDRAM refresh.
The bus release by the BREQ and BACK signal handshaking requires some overhead. If the slave
has many tasks, multiple bus cycles should be executed in a bus mastership acquisition. Reducing
the cycles required for master to slave bus mastership transitions streamlines the system design.
CKIO
BREQ
BACK
A25 to A0
D31 to D0
CSn
Other bus
control signals
Figure 12.46 Bus Arbitration Timing
12.5.12 Others
Reset: The bus state controller (BSC) can be initialized completely only at power-on reset. At
power-on reset, all signals are negated and output buffers are turned off regardless of the bus cycle
state. All control registers are initialized. In standby, sleep, and manual reset, control registers of
the bus state controller are not initialized. At manual reset, the current bus cycle being executed is
completed and then the access wait state is entered. If a 16-byte transfer is performed by a cache
or if another LSI on-chip bus master module is executed when a manual reset occurs, the current
access is cancelled in longword units because the access request is cancelled by the bus master at
manual reset. If a manual reset is requested during cache fill operations, the contents of the cache
cannot be guaranteed. Since the RTCNT continues counting up during manual reset signal
assertion, a refresh request occurs to initiate the refresh cycle. Note, however, a bus arbitration
request by the BREQ signal can’t be accepted during manual reset signal assertion.
Some flash memories may specify a minimum time from reset release to the first access. To
ensure this minimum time, the bus state controller supports a 5-bit reset wait counter (RWTCNT).
At power-on reset, the RWTCNT is cleared to 0. After a power-on reset, RWTCNT is counted up
synchronously together with CKIO and an external access will not be generated until RWTCNT is
counted up to H′007F. At a manual reset, RWTCNT is not cleared. RWTCNT cannot be read from
or written to.
Rev. 1.00 Dec. 27, 2005 Page 456 of 932
REJ09B0269-0100