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On a typical microprocessor, a distinct I/O address is used to refer to
the I/O data registers and a distinct address for the control and
status registers in an I/O controller for a given device. Such
registers are refered to as ports. In intel 8088, two I/O instruction
formats are used. In one format, the 8-bit opcode specifies an dI/O
operation; this is followed by an 8-bit port address. Other I/O opcodes
imply that the port address is in the 16-bit DX register. How many
ports can the 8088 address in each I/O addressing mode???
Thank you!

Computer Freak wrote:

On a typical microprocessor, a distinct I/O address is used to refer to
the I/O data registers and a distinct address for the control and
status registers in an I/O controller for a given device. Such
registers are refered to as ports. In intel 8088, two I/O instruction
formats are used. In one format, the 8-bit opcode specifies an dI/O
operation; this is followed by an 8-bit port address. Other I/O opcodes
imply that the port address is in the 16-bit DX register. How many
ports can the 8088 address in each I/O addressing mode???
Thank you!

If it is a serial port, then obviously just one at a time.
However on a parallel port, it can control up to 7 or 15
devices simultaneously (device 0 is reserved as the cpu id).

Eric

"Computer Freak" <nivine.dalleh@gmail.com> wrote in message
news:1135692298.276122.236080@g49g2000cwa.googlegroups.com...

On a typical microprocessor, a distinct I/O address is used to refer to
the I/O data registers and a distinct address for the control and
status registers in an I/O controller for a given device. Such
registers are refered to as ports. In intel 8088, two I/O instruction
formats are used. In one format, the 8-bit opcode specifies an dI/O
operation; this is followed by an 8-bit port address. Other I/O opcodes
imply that the port address is in the 16-bit DX register. How many
ports can the 8088 address in each I/O addressing mode???
Thank you!

In the former case, the processor can address 8 ports, one for each bit.
The ports are enabled by setting a bit corresponding to the port.

In the second case, which works much the same, 64 ports can be addressed.
The first byte on the bus selects one of eight groups of eight ports.
The second byte selects the port within the group.

del cecchi

"Computer Freak" <nivine.dalleh@gmail.com> wrote in message
news:1135692298.276122.236080@g49g2000cwa.googlegroups.com...

On a typical microprocessor, a distinct I/O address is used to refer to
the I/O data registers and a distinct address for the control and
status registers in an I/O controller for a given device. Such
registers are refered to as ports. In intel 8088, two I/O instruction
formats are used. In one format, the 8-bit opcode specifies an dI/O
operation; this is followed by an 8-bit port address. Other I/O opcodes
imply that the port address is in the 16-bit DX register. How many
ports can the 8088 address in each I/O addressing mode???
Thank you!

This is a trick question. Obviously each addressing mode addresses one port.

P