108
6.2.4
Bus Release Control Register (BRCR)
BRCR is an 8-bit readable/writable register that enables address output on bus lines A
23
to A
20
and
enables or disables release of the bus to an external device.
7
A23E
1
—
1
R/W
Address 23 to 20 enable
These bits enable PA
7
to PA
4
to be
used for A
23
to A
20
address output
6
A22E
1
—
1
R/W
5
A21E
1
—
1
R/W
4
A20E
1
—
0
—
3
—
1
—
1
—
2
—
1
—
1
—
1
—
1
—
1
—
0
BRLE
0
R/W
0
R/W
Bit
Modes
1 and 2
Initial value
Read/Write
Initial value
Read/Write
Modes
3 and 4
Reserved bits
Bus release enable
Enables or disables release
of the bus to an external device
BRCR is initialized to H'FE in modes 1 and 2, and to H'EE in modes 3 and 4, by a reset and in
hardware standby mode. It is not initialized in software standby mode.
Bit 7—Address 23 Enable (A23E): Enables PA
4
to be used as the A
23
address output pin.
Writing 0 in this bit enables A
23
output from PA
4
. In modes other than 3 and 4, this bit cannot be
modified and PA
4
has its ordinary port functions.
Bit 7
A23E
Description
0
PA
4
is the A
23
address output pin
1
PA
4
is an input/output pin
(Initial value)
Bit 6—Address 22 Enable (A22E): Enables PA
5
to be used as the A
22
address output pin.
Writing 0 in this bit enables A
22
output from PA
5
. In modes other than 3 and 4, this bit cannot be
modified and PA
5
has its ordinary port functions.
Bit 6
A22E
Description
0
PA
5
is the A
22
address output pin
1
PA
5
is an input/output pin
(Initial value)
Summary of Contents for H8/3008
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