Test: Interfacing With 8051 Ports - Computer Science Engineering (CSE) MCQ

The SFR addresses of the ports P0, P1, P2 and P3 are 80H, 90H, A0H and B0H respectively.

Each port line of a port can individually source a current of upto 0.5 mA.

Each port line of a port can individually sink a current of upto 8 mA.

When a logic 0 is sent to a port line as an output port, it can sink 8 LS TTL inputs. Port 0 is used as data bus during external interfacing whenever required.

 Port 0 is an open drain bidirectional (input or output) port with internal pullups. Port 1, Port 2, Port 3 are 8-bit bidirectional ports.

The ports P1, P2 and P3 can source or sink 4 LS TTL inputs when being used as an output port on each of its line.

Port 3 pins which are externally pulled low when being used as input pins will source current of 500 micro amperes.

 For interfacing external program memory, EA(active low) pin must be grounded. If the EA(active low) signal is grounded then the execution will start directly from the 16-bit address 0000H in external program memory.

 If EA(active low) signal =1, then the execution starts from an internal EPROM or flash RAM address 000H, can continue upto FFFH address and then for higher addresses it will go into external memory.

The EA(active low) pin is grounded for interfacing external EPROM. The PSEN(active low) is used for interfacing EPROM i.e. it acts as an OE(active low) input to EPROM.

The unit(LED) glows for a duration of 5 msec.

Starting from either right most or left most digit, every digit glows for 5 msec one by one. Thus one scan of the 8 digit display requires 40 msec. Thus in one second, 25 scans of the complete 8-digit display can be carried out.

the DAC 0808 is connected with OPAMP externally, to convert its current output into voltage.

For appropriate glow, a LED typically requires 8-10 mA with around 1.6 Volts.

If 8 LEDs are connected to a port of 8051, and if all are expected to glow simultaneously, the total current sinked by the 8051 port will be 8×8=64 mA (since min voltage for an LED to glow=8 mA) which is less than the maximum 71 mA.