[TUHS] who invented the link register

Larry Stewart stewart at serissa.com
Wed Oct 26 21:12:40 AEST 2022

Whirlwind I had a TD (transfer digits) instruction that stored only the low 11 bits from the accumulator to storage

> On Oct 26, 2022, at 12:45 AM, Ralph Corderoy <ralph at inputplus.co.uk> wrote:
> Hi Lawrence,
>> With the new SP and TA, one would use SP to call a subroutine, and the
>> first instruction of any subroutine would be TA to save the return
>> address into the final location of the subroutine.  (TA only modified
>> the low 11 bits of the 16 bit location)
>> Before these instructions, a subroutine call would require one
>> additional memory location, to hold the return address for each point
>> of call, and one additional instruction, one to load the return
>> address into the accumulator and one to store it into the code at the
>> end of the subroutine.  (The latter could be the first instruction of
>> the subroutine.)
> So before SP and TA, would the ‘latter’ instruction at the start of the
> subroutine, which stores the accumulator holding the return address, be
> modifying all sixteen bits of the location unlike TA which only modifies
> the bottom eleven?
> If so, did the accumulator's top bits hold the ‘return’ op-code or was
> there another instruction near the subroutine's end which loaded the
> 11-bit address before a second instruction jumped to it?
> -- 
> Cheers, Ralph.

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