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3815Re: [Altair Computer Club] Strange discovery with stop + reset, run and Bytesaver

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  • B Degnan
    Jul 25, 2014
    • 0 Attachment
      (with same card installed in my Altair I mean, apples to apples.).  Do you have a picture of the added jumper?

      -----Original Message-----
      From: B Degnan billdeg@... [altaircomputerclub] <altaircomputerclub@yahoogroups.com>
      To: altaircomputerclub <altaircomputerclub@yahoogroups.com>
      Sent: Fri, Jul 25, 2014 10:18 am
      Subject: Re: [Altair Computer Club] Strange discovery with stop + reset, run and Bytesaver

      Is the ROM code on the Yahoo site? I'd be happy to test my system if you'd like/compare contrast to confirm.

      -----Original Message-----
      From: Craig Landrum craigl@... [altaircomputerclub] <altaircomputerclub@yahoogroups.com>
      To: altaircomputerclub <altaircomputerclub@yahoogroups.com>
      Sent: Fri, Jul 25, 2014 9:39 am
      Subject: Re: [Altair Computer Club] Strange discovery with stop + reset, run and Bytesaver

      > Can anyone shed any light on how my machine is capable 
      > of jumping to the rom card?
      It probably depends on your RAM configuration and what kind of card(s) comprise your RAM. Two thoughts occur to me - with all switches down, you would normally be starting execution at address 0000. If that address contained a 0 (which is an 8080/Z80 NOP) instruction, it would simply advance the PC + 1 and fetch the next instruction. If all of your RAM came up initialized to zero, you would end up executing about 57,344 NOPs before you hit the first non-zero executable code at E000. On the other hand, perhaps your RAM at address 0000 initializes to FFh. In that case the processor would execute an RST 7 instruction which (if my aging memory serves me) effectively does a CALL 0038H, which means the processor begins executing instructions at 0038h. If that address were to contain something like C3 00 E0... (i.e. JMP E000 ), that would go directly to your EPROM at E000. The Z80 (not sure about the 8080) also had an interrupt mode whereby an interrupting device could supply a portion of the address to which the processor would jump to service the interrupt. The Z80 systems we built back in the day depended on this capability which worked quite well. Probably not involved in what you are seeing however. -- Craig Landrum Chief Technical Officer mindwrap, inc. Phone: (540) 347-2552 x 229 Fax: (540) 347-2556 email: craigl@... ------------------------------------ Posted by: Craig Landrum <craigl@...> ------------------------------------ ------------------------------------ Yahoo Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/altaircomputerclub/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/altaircomputerclub/join (Yahoo! ID required) <*> To change settings via email: altaircomputerclub-digest@yahoogroups.com altaircomputerclub-fullfeatured@yahoogroups.com <*> To unsubscribe from this group, send an email to: altaircomputerclub-unsubscribe@yahoogroups.com <*> Your use of Yahoo Groups is subject to: https://info.yahoo.com/legal/us/yahoo/utos/terms/

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