22-06-2013, 04:33 PM
Programmable Peripheral Interface
[attachment=55890]
Logic Circuit
Inputs to the Logic Circuit
address lines A15 - A2 (the I/0 address space is 216 addresses, and A1 and A0 are used for the chip’s address lines)
the 8088’s IO/M line HIGH denotes an IO instruction (IN, OUT) LOW denotes a memory access instruction (i.e., MOV)
Output of the logic circuit
a single low value from the 15 inputs (a NAND or OR gate) to activate the Chip Select
The connections for A15-A2 fix the chip’s address in I/O space
Minimum mode
In minimum mode, the 8088 is the only microprocessor in the circuit. It can assume that it has control of memory, address, and data buses
In maximum mode, the 8088 is configured for multiple microprocessors. The function of pins is changed to provide processor-to-processor communication
Reset
A single reset line is connected to all chips in the system (8088, 8255, 8253, etc.)
Reset puts the chip in a known state
Pushing the reset button on your computer generally activates a 555 timer circuit that outputs a high pulse for a short period of time
On Reset, the 8088 goes to fixed addresses (ROM chips) where boot sequence instructions are stored.
[attachment=55890]
Logic Circuit
Inputs to the Logic Circuit
address lines A15 - A2 (the I/0 address space is 216 addresses, and A1 and A0 are used for the chip’s address lines)
the 8088’s IO/M line HIGH denotes an IO instruction (IN, OUT) LOW denotes a memory access instruction (i.e., MOV)
Output of the logic circuit
a single low value from the 15 inputs (a NAND or OR gate) to activate the Chip Select
The connections for A15-A2 fix the chip’s address in I/O space
Minimum mode
In minimum mode, the 8088 is the only microprocessor in the circuit. It can assume that it has control of memory, address, and data buses
In maximum mode, the 8088 is configured for multiple microprocessors. The function of pins is changed to provide processor-to-processor communication
Reset
A single reset line is connected to all chips in the system (8088, 8255, 8253, etc.)
Reset puts the chip in a known state
Pushing the reset button on your computer generally activates a 555 timer circuit that outputs a high pulse for a short period of time
On Reset, the 8088 goes to fixed addresses (ROM chips) where boot sequence instructions are stored.