LSI Symbios SYM53C040, Technical Manual

Page: 144 / 214

8-18 System Registers
Register: 0xFF21
Multipurpose I/O Bank 3 Enable (MPE3)
Read/Write
R Reserved [7:4]
MPE3_[3:0] Multipurpose I/O Bank 3 Enable [3:0]
These bits control the output enables on the I/O pins
MPIO3_0, MPIO3_1, MPIO3_2, and MPIO3_3. A value of
1 turns on the pin driver, and a value of 0 3-states the
pin. Because the value in this register powers up to all
zeros, the pins will initially be 3-stated at power-up.
These pins also have internal 100
µ
A pull-down resistors,
which can be disabled with the Multipurpose I/O Bank 3
Pull-down Enable (MPPE3) register ( 0xFF25 ).
When the SPEN bit (0xFF05, bit 1) is set, the MPIO3_2
pin is mapped to the TXD serial port function of the
microcontroller core, and the MPIO3_3 pin is mapped to
the RXD serial port function of the microcontroller core.
When the EIEN bit (0xFF05, bit 0) is set, the MPIO3_0
pin is mapped to the EXS0_INT external interrupt
function of the microcontroller core and the MPIO3_1 pin
is mapped to the EXS1_INT external interrupt function of
the microcontroller core.
7 4 3 2 1 0
R MPE3_3 MPE3_2 MPE3_1 MPE3_0
Defaults:
0 0 0 0 0 0 0 0