8085 Address Decoding
Adrian Graham
witchy at binarydinosaurs.co.uk
Thu Jan 26 02:41:29 CST 2017
On 26/01/2017 01:09, "Alexis Kotlowy" <thrashbarg at kaput.homeunix.org> wrote:
>> My Executel ROM disassembly puts this block of code between 0x0F38 and
>> 0x0F3E:
>>
>> 0F38 L0F38:
>> 0F38 : 7B "{" [4] mov a,e
>> 0F39 : 95 " " [4] sub l
>> 0F3A : 5F "_" [4] mov e,a
>> 0F3B : 7A "z" [4] mov a,d
>> 0F3C : 9C " " [4] sbb h
>> 0F3D : 57 "W" [4] mov d,a
>> 0F3E : C9 " " [10] ret
>>
>> Does that make sense? I might not have a full disassembly since L0F38 is
>> only called from two places and neither of them jump back to 0x0FB2 but I
>> know that doesn't necessarily mean it's wrong.
>>
>> Cheers,
>>
>
> Hi Adrian,
>
> The instruction at 0x0F3E is RET, so it's going to read two bytes off
> the stack and jump to it. This is what you're seeing at 0xF0B2 and
> 0xF0B3. I'd suggest you look at how RAM is addressed at the top of
> memory space and see if it's correct.
I was afraid someone might say that. Whilst I don't have a memory map for
this system (or any other docs apart from the ones I'm writing myself) I did
notice last night that CAS-1 was missing. RAM is laid out like a CBM PET
with 16x 4116 DRAMs split into lower and upper blocks. RAS and CAS-0 are
pulsing.
More probing tonight then!
--
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
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