144
7.2.5
Bus Control Register L (BCRL)
7
BRLE
0
R/W
6
BREQOE
0
R/W
5
—
0
—
4
OES
0
R/W
3
DDS
1
R/W
0
WAITE
0
R/W
2
RCTS
0
R/W
1
WDBE
0
R/W
Bit
Initial value
R/W
:
:
:
BCRL is an 8-bit readable/writable register that performs selection of the external bus-released
state protocol, enabling or disabling of the write data buffer function, and enabling or disabling of
WAIT
pin input.
BCRL is initialized to H'08 by a power-on reset and in hardware standby mode. It is not initialized
by a manual reset or in software standby mode.
Bit 7—Bus Release Enable (BRLE): Enables or disables external bus release.
Bit 7
BRLE
Description
0
External bus release is disabled.
BREQ
,
BACK
and
BREQO
can be used as I/O ports.
(Initial value)
1
External bus release is enabled.
Bit 6—BREQO Pin Enable (BREQOE): Outputs a signal that requests the external bus master
to drop the bus request signal (
BREQ
) in the external bus release state, when an internal bus
master performs an external space access, or when a refresh request is generated.
Bit 6
BREQOE
Description
0
BREQO
output disabled.
BREQO
can be used as I/O port.
(Initial value)
1
BREQO
output enabled.
Bit 5—Reserved: This bit cannot be modified and is always read as 0.
Bit 4—OE Select (OES): Selects the
CS3
pin as the
OE
pin.
Bit 4
OES
Description
0
Uses the
CS3
pin as the port or as
CS3
signal output
(Initial value)
1
When only area 2 is set for DRAM, or when areas 2 to 5 are set as
contiguous DRAM space, the
CS3
pin is used as the
OE
pin.