Explain the alternate function of port 3
Answers
Answered by
0
I think so. The structure of a Port-0 pin is shown in fig 6.It has 8 pins (P0.0-P0.7).
Add caption
Port-0 can be used as a normal bidirectional I/O port or it can be used for address/data interfacing for accessing external memory. When control is '1', the port is used for address/data interfacing. When the control is '0', the port can be used as a bidirectional I/O port.
PORT 0 as an Input Port
Let us assume that control is '0'. When the port is used as an input port, '1' is written to the latch. In this situation both the output MOSFETs are 'off'. Hence the output pin have floats hence whatever data written on pin is directly read by read pin.

PORT 0 as an Output Port
Suppose we want to write 1 on pin of Port 0, a '1' written to the latch which turns 'off' the lower FET while due to '0' control signal upper FET also turns off as shown in fig. above. Here we wants logic '1' on pin but we getting floating value so to convert that floating value into logic '1' we need to connect the pull up resistor parallel to upper FET . This is the reason why we needed to connect pull up resistor to port 0 when we want to initialize port 0 as an output port .

If we want to write '0' on pin of port 0 , when '0' is written to the latch, the pin is pulled down by the lower FET. Hence the output becomes zero.

When the control is '1', address/data bus controls the output driver FETs. If the address/data bus (internal) is '0', the upper FET is 'off' and the lower FET is 'on'. The output becomes '0'. If the address/data bus is '1', the upper FET is 'on' and the lower FET is 'off'. Hence the output is '1'. Hence for normal address/data interfacing (for external memory access) no pull-up resistors are required.Port-0 latch is written to with 1's when used for external memory access.
Add caption
Port-0 can be used as a normal bidirectional I/O port or it can be used for address/data interfacing for accessing external memory. When control is '1', the port is used for address/data interfacing. When the control is '0', the port can be used as a bidirectional I/O port.
PORT 0 as an Input Port
Let us assume that control is '0'. When the port is used as an input port, '1' is written to the latch. In this situation both the output MOSFETs are 'off'. Hence the output pin have floats hence whatever data written on pin is directly read by read pin.

PORT 0 as an Output Port
Suppose we want to write 1 on pin of Port 0, a '1' written to the latch which turns 'off' the lower FET while due to '0' control signal upper FET also turns off as shown in fig. above. Here we wants logic '1' on pin but we getting floating value so to convert that floating value into logic '1' we need to connect the pull up resistor parallel to upper FET . This is the reason why we needed to connect pull up resistor to port 0 when we want to initialize port 0 as an output port .

If we want to write '0' on pin of port 0 , when '0' is written to the latch, the pin is pulled down by the lower FET. Hence the output becomes zero.

When the control is '1', address/data bus controls the output driver FETs. If the address/data bus (internal) is '0', the upper FET is 'off' and the lower FET is 'on'. The output becomes '0'. If the address/data bus is '1', the upper FET is 'on' and the lower FET is 'off'. Hence the output is '1'. Hence for normal address/data interfacing (for external memory access) no pull-up resistors are required.Port-0 latch is written to with 1's when used for external memory access.
Similar questions