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
address output from PA
6
. In modes other than 3, 4, and 6 this bit
cannot be modified and PA
6
has its ordinary input/output functions.
Bit 5
A21E
Description
0
PA
6
is the A
21
address output pin
1
PA
6
is the PA
6
/TP
6
/TIOCA
2
input/output pin
(Initial value)
Bits 4 to 1—Reserved: Read-only bits, 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
(Initial value)
can be used as input/output pins
1
The bus can be released to an external device
6.2.6 Chip Select Control Register (CSCR)
CSCR is an 8-bit readable/writable register that enables or disables output of chip select signals
(CS
7
to CS
4
).
If a chip select signal (CS
7
to CS
4
) output is selected in this register, the corresponding pin
functions as a chip select signal (CS
7
to CS
4
) output, this function taking priority over other
functions. CSCR cannot be modified in single-chip mode.
CSCR is initialized to H'0F by a reset and in hardware standby mode. It is not initialized in
software standby mode.
Bit
Initial value
Read/Write
7
CS7E
0
R/W
6
CS6E
0
R/W
5
CS5E
0
R/W
4
CS4E
0
R/W
3
—
1
—
0
—
1
—
2
—
1
—
1
—
1
—
Chip select 7 to 4 enable
These bits enable or disable
chip select signal output
Reserved bits
119
www.DataSheet4U.com