109
Bit 5—Address 21 Enable (A21E): Enables PA
6
to be used as the A
21
address output pin.
Writing 0 in this bit enables A
21
output from PA
6
. In modes other than 3 and 4, this bit cannot be
modified and PA
6
has its ordinary port functions.
Bit 5
A21E
Description
0
PA
6
is the A
21
address output pin
1
PA
6
is an input/output pin
(Initial value)
Bit 4—Address 20 Enable (A20E): Enables PA
7
to be used as an address output pin. When 0 is
written to this bit, PA
7
functions as address output A
20
. In modes 3 and 4, PA
7
functions as an
address output pin, and in modes 1 and 2, as a normal port pin.
Bit 4
A20E
Description
0
PA
7
is the A
20
address output pin (In mode 3 or 4)
1
PA
7
is an input/output pin (In mode 1 or 2)
Bits 3 to 1—Reserved: These bits cannot be modified and are always read as 1.
Bit 0—Bus Release Enable (BRLE): Enables or disables release of the bus to an external device.
Bit 0
BRLE
Description
0
The bus cannot be released to an external device
BREQ
and
BACK
can be used as input/output pins
(Initial value)
1
The bus can be released to an external device
6.2.5
Bus Control Register (BCR)
—
—
RDEA
WAITE
1
Initial value
1
0
*
1
0
*
1
0
*
1
1
*
2
1
0
Read/Write
—
—
R/W
R/W
R/W
R/W
—
—
7
6
5
4
3
2
1
0
ICIS1
ICIS0
—
—
Bit
Notes: 1. 1 must not be written in bits 5 to 3.
2. 0 must not be written in bit 2.
BCR is an 8-bit readable/writable register that enables or disables idle cycle insertion, selects the
area division unit, selects the extended memory map, and enables or disables
WAIT
pin input.
Summary of Contents for H8/3008
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