S0 and S1 : The status of the system bus is difined by the S0 and S1 lines as follows -
S1 |
S0 |
Operation Specified |
0 |
0 |
Halt |
0 |
1 |
Memory or I/O WRITE |
1 |
0 |
Memory or I/O READ |
1 |
1 |
Instruction Fetch |
There are ten lines associated with CPU and bus control-
- TRAP , RST7.5 , RST6.5 , RST5.5 and INTR are the Interrupt lines.
- INTA: Interrupt acknowledge line.
- RESET IN : This is the reset input signal to the 8085.
- RESET OUT : The 8085 generates the RESET-OUT signal in response to RESET-IN signal , which can be used as a system reset signal .
- HOLD : HOLD signal is used for DMA request.
- HLDA : HLDA signal is used for DMA grant .
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