Page 127 - Digital Electronics by harish
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The signal diagram is shown in figure 5.4.
Figure 5.4 : Signal diagram of Intel 8085 microprocessor
Pin Description
number Signal name
Address Bus
Higher order byte (8 bits) of address bus. The address bus
21 – 28 A 8 – A 15 is unidirectional (one-way, ie. microprocessor to memory).
Multiplexed Address / Data bus
Lower order byte (8 bits) address bus (A 0 - A 7).
And
12 -19 AD 0 – AD 7 Data bus (8 bits) (D 0 – D 7).The data bus is bidirectional
(two-wayie. microprocessor to memory and memory to
microprocessor).
Control and Status signals
ALE - Address Latch Enable.
Used for de-multiplexing the Address / Data bus. i.e.
30 ALE separating the lower order address lines (A 0 – A 7) and data
lines (D 0 – D 7) from (AD 0 – AD 7).
29 S 0 The microprocessor indicates its status (memory write,
33 S 1 memory read, I/O write, I/O read, Opcode fetch, Halt,
Hold, Reset) through these three output pins. IO/ will be
34 IO / „1‟ for I/O operation and „0‟ for memory operation.
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