Timeline for 8085 MPU; Stepping through an instruction (Timing diagrams)
Current License: CC BY-SA 4.0
9 events
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| Jun 11, 2020 at 15:10 | history | edited | CommunityBot |
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| Aug 23, 2019 at 23:47 | vote | accept | Aravindh Vasu | ||
| Aug 23, 2019 at 20:14 | comment | added | jonk | @AravindhVasu The B register has to be addressed (it's in a register file with more than one register.) How exactly that works is a detail left to the designers. But it must be done, somehow. That addressed value will have to pass through a tri-state buffer to the bus, which has to be enabled. Then the temp register has to latch that bus value. The decoding process sets all this up with, often, a state machine and control line outputs derived from that. Most of the complicating details are swept under the "decoder and state machine" rug. The rest always looks clean and easy. | |
| Aug 23, 2019 at 9:50 | comment | added | Aravindh Vasu | Yeah I get that the ALU cannot keep on putting values on the bus,I meant, that's the reason why we put a buffer in-between the bus and the ALU, right? When is the B register value transferred to the temporary register? One more question: What do you mean by "decide", what is the internal process of deciding? I mean, if it had to take more T-states, how will it "decide" and what does "Float MARL" mean? | |
| Aug 23, 2019 at 9:43 | comment | added | jonk | @Aravindh The ALU will have its own opcode to tell it to add or subtract or perform some logical operation. Decoding the instruction will work that out as part of the decoding process. Sure, the ALU can continually perform, but you cannot always allow its output to drive the internal bus which may be in use for some other reason. The MDR is the "memory data register." | |
| Aug 23, 2019 at 9:36 | comment | added | Aravindh Vasu | Thank you very much for answering, I'm very new to digital electronics, so please bare with my naivety here; what do you mean by "set up ALU opcode value"? When is the B register addressed and the contents are transferred to the temp reg? This is the final step right? as the ALU constantly calculates the sum of the two(does it, that is why we have a buffer right?) What does MDR basically do? | |
| Aug 23, 2019 at 8:47 | history | edited | jonk | CC BY-SA 4.0 |
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| Aug 23, 2019 at 8:42 | history | edited | jonk | CC BY-SA 4.0 |
added 3 characters in body
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| Aug 23, 2019 at 8:36 | history | answered | jonk | CC BY-SA 4.0 |