ALE pin in 8085 Microprocessor

MicrocontrollerMicroprocessor8085

Intel 8085 is an 8-bit microprocessor which has 16 address line for 16-bit address of a memory location. 8 higher order address bits are transferred through 8 bit lines out of this 16 address line while remaining lower order 8 bits of the address are sent through another 8 lines multiplexed with the 8-bit data lines. ALE (Address Enable Latch) is the control signal which is nothing but a positive going pulse generated when a new operation is started by microprocessor. So when pulse goes high means ALE=1, it makes address bus enable and when ALE=0, means low pulse makes data bus enable.

Fig: Pin diagram of 8085

Let us consider this following example and also the voltage level at ALE pin. If we consider instruction MVI E, ABH then it means that ABH will be moved or copied to the register E. And as a result the previous value of E will get over written.

Address
Hex Codes
Mnemonic
Comment
2000
1E
MVIE, ABH
E ← ABH
2001
AB


ABH as operand

This instruction will have seven T-states as shown below.

Summary  − So this instruction MVI E, ABH requires 2-Bytes, 2-Machine Cycles Opcode Fetch and Memory Read) and 7 T-States for execution as shown in the timing diagram.

raja
Published on 03-Jan-2019 17:03:09
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