73M2910L

Microcontroller

8

USR3 I/O Port Direction (DIR3) External Address 0001h

Byte Addressable

Reset State FFh

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

DIR3.7

DIR3.6

DIR3.5

DIR3.4

DIR3.3

DIR3.2

DIR3.1

DIR3.0

This register is used to designate the USR3 pins as either inputs or outputs. If the register bit is reset to a 0, the

corresponding USR3 pin is programmed as an output that will be driven by the corresponding USR3 data

register bit. If the register bit is a 1, the corresponding pin will be treated as an input.

After a reset, the USR3 pins will present a high impedance output state and the input values will not be driven

from the pin, but will be driven to a 1 internally. The pins will assume normal I/O operation once the processor

has written the USR3 port direction register. This feature will ensure a low current state at reset.

If the bank select feature is chosen, USR3.7 pin is forced to be an output.

BANK SELECT (BNKSEL) EXTERNAL ADDRESS 0002h

Byte Addressable

Reset State 00h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

B7

B6

B5

B4

B3

BSEN

BS1

BS0

This register is used to accommodate systems where more than 64 kBytes (up to 128 kBytes) of program

memory are required. Pin USR3.7 acts as an address pin, A16, if BSEN is set to a 1 and the processor is

fetching an instruction and not data memory. If BSEN is set to a 1, A15 is also modified during instruction

fetches as shown below. If BSEN is a 0, no alterations to address bit A15 are made, and pin USR3.7 is a

function of USR3 bit 7 and DIR3 bit 7.

Bits (7:3) are general purpose read/write register bits.

A15

Value of the 16th address bit as it appears at pin A15.

A15’

Address from port 2 internal logic, the value that will appear as the most significant address bit if no

bank select feature is chosen.

A16

Value of the 17th and MSB of the instruction address seen at the USR3.7 port pin, if the bank select

feature is selected. If the bank select feature is not selected, USR3.7 acts as a normal USR3 I/O port

pin.