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| [165] instruction register http://forum.6502.org/viewtopic.php?f=7&t=420 |
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| Author: | Klobs [ Sat Jul 06, 2002 3:08 pm ] |
| Post subject: | [165.1] instruction register |
hi, why ist the instruction register of the mos 6502 not connected to the databus (internal). Perhaps the hardware could be realized cheaper? |
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| Author: | GARTHWILSON [ Mon Jul 08, 2002 6:19 pm ] |
| Post subject: | [165.2] instruction register |
> hi, > why ist the instruction register of the mos 6502 not connected to > the databus (internal). Perhaps the hardware could be realized > cheaper? Since I am not sure I understand what you are asking, I would normally ask for clarificaion by private E-mail without burdening the list with it. That option does not seem to be available anymore with Delphi's basic service. Do you have an architectural diagram of the processor? There's no reason to have the instruction register go to the internal data bus so instructions can be latched into any of the other registers besides the ones in the instruction-decode logic, which does do some pipelining. In the case of something like LDA #20h, The LDA# (op code $A9) is regarded as the instruction, and the $20 is regarded as data. The two-byte instrucion takes 2 clocks, or 1 microsecond at 2MHz. Many of the 6502 instructions, including this example, have no dead bus cycles. Garth |
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