re: A86: RAM Page $80 ??

To: assembly-86@lists.ticalc.org
Subject: re: A86: RAM Page $80 ??
From: Dan Eble <eble@cis.ohio-state.edu>
Date: Tue, 12 Aug 1997 15:05:57 -0400 (EDT)
In-Reply-To: <BMSMTP87141623628a0734985@dpcs4.itg.ti.com>
Reply-To: assembly-86@lists.ticalc.org

On Tue, 12 Aug 1997, Pat Milheron wrote:

>
> You are right this is not the exact code you had seen. 
> 

That sounds like a challenge. :)
Here is the exact disassembly from ROM page A, with comments added.

6940  6F           LD   L,A        ; load A from table at $6B00
6941  26 00        LD   H,0
6943  11 00 6B     LD   DE,$6B00
6946  19           LD   ADD HL,DE
6947  7E           LD   A,(HL)
6948  B7           OR   A          ; only continue if A != 0
6949  CA AD 68     JP   Z,$68AD
694C  57           LD   D,A        ; save table value
694D  DB 06        IN   A,(6)      ; save current RAM page
694F  F5           PUSH AF
6950  3E 80        LD   A,$80      ; here's the weird part
6952  D3 06        OUT  (6),A
6954  7A           LD   A,D        ; restore table value
6955  32 00 80     LD   ($8000),A
6958  F1           POP  AF
6959  D3 06        OUT  (6),A      ; restore previous RAM page
695B  7A           LD   A,D        ; restore table value
695C  C9           RET

>
> Valid values to be written to this port are 41h - 47h, ram pages 1 - 7.
> 

Yet there's this code on page A.  Maybe it's a red herring like DO BE DO 
BE DO (see comment below).

> 
> P.S. DO BE DO BE DO
> 

That sounds like a taunt... or a hint. :)

--------
Dan Eble (mailto:eble@cis.ohio-state.edu)
         (http://www.cis.ohio-state.edu/~eble)

References:

re: A86: RAM Page $80 ??

From: Pat Milheron <pmilheron@ti.com>