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SH7751 Group, SH7751R Group
Section 13 Bus State Controller (BSC)
R01UH0457EJ0301 Rev. 3.01
Page 495 of 1128
Sep 24, 2013
13.3.14
Cooperation between Master and Slave
To enable system resources to be controlled in a harmonious fashion by master and slave, their
respective roles must be clearly defined. Before DRAM or synchronous DRAM is used,
initialization operations must be carried out. Responsibility must also be assigned when a standby
operation is performed to implement the power-down state.
The design of this LSI provides for all control, including initialization, refreshing, and standby
control, to be carried out by the master mode device.
If this LSI is specified as the master in a power-on reset, it will not accept bus requests from the
slave until the
BREQ
enable bit (BCR1.BREQEN) is set to 1.
To ensure that the slave processor does not access memory requiring initialization before use, such
as DRAM and synchronous DRAM, until initialization is completed, write 1 to the
BREQ
enable
bit after initialization ends.
Before setting self-refresh mode in standby mode, etc., write 0 to the
BREQ
enable bit to
invalidate the
BREQ
signal from the slave. Write 1 to the
BREQ
enable bit only after the master
has performed the necessary processing (refresh settings, etc.) for exiting self-refresh mode.
13.3.15
Notes on Usage
Refresh:
Auto refresh operations stop when a transition is made to standby mode, hardware
standby mode, or deep-sleep mode. If the memory system requires refresh operations, set the
memory in the self-refresh state prior to making the transition to standby mode, hardware standby
mode, or deep-sleep mode.
Bus Arbitration:
On transition to standby mode or deep-sleep mode, the processor in master
mode does not release bus privileges. In systems performing bus arbitration, make the transition to
standby mode or deep-sleep mode only after setting the bus privilege release enable bit
(BCR1.BREQEN) to 0 for the processor in master mode. If the bus privilege release enable bit
remains set to 1, operation cannot be guaranteed when the transition is made to standby mode or
deep-sleep mode.
Simultaneous Use of Refresh and Bus Arbitration:
With the SH7751, when performing bus
arbitration using the external device and
BREQ
signal, the following two failures may occur.
•
When a
BREQ
signal is input from the external device while using DMA transfer or target
transfer by the PCIC, and DRAM/synchronous DRAM is set to CAS-before-RAS refresh and
auto-refresh in master mode (MD7 = 1), bus arbitration may not be performed correctly and
this LSI may hang up.