Tektronix 4051 magic mode found!

From: Philip.Belben_at_pgen.com <(Philip.Belben_at_pgen.com)>
Date: Wed Feb 24 11:22:38 1999

>>
>> Try "Exec". I don't have any details of how to use it, sorry. Let me know
>> what you find out.
>>
>
> Hmmm...this brings back some memories. From my recollection, this
> statement accepted a string argument. The character string supplied
> was coded in a special pseudo-hexadecimal:
>
> 0="0", 1="1", 2="2", 3="3", 4="4", 5="5", 6="6", 7="7"
> 8="8", 9="9", a=":", b=";" c="<", d="=", e=">", f="?"
>
> For example, to represent the hex sequence 6e7f391d, the string would be
> "6>7?391="
>
> Each two characters represent a byte.
>
> Now, using this method, you could 'code' 6800 machine code instructions.
>
> The EXEC statement would store the bytes supplied in the string argument
> as a linear sequence of machine code, and cause a jump to the segment
> of code. I don't recall if it was JMP'd to, or JSR'd to...and don't
> remember any of the details of how to return from a segment of code
> executed with the EXEC statement. Obviously, sending random stuff
> to an EXEC statement could wedge the machine up.
>
> I remember that EXEC was used frequently by folks who were experts
> with the machine (and had magic lists of the internal runtime
> calls) to make game programs and stuff in machine code that would
> run much faster than the interpreted BASIC. It also allowed
> 'extensions' to BASIC that you could use to do things like PEEK and POKE,
> etc. There were conventions for passing variables in and out of
> EXEC'd code, so BASIC could be used for 'high level' functions, and
> the fast EXEC'd machine code could be used for time-critical or
> other functions that were too slow, or too tedious (IE: bit manipulation)
> to do in BASIC.
>
> Hope this helps. It's all from foggy memories..all the fun with 4051's
> that I had happened sometime around 1978...21 years ago. I'm amazed
> that I can remember ANY of it, given that many times I can't remember
> where I put my car keys :-)

Rick, you wonderful person! I wonder what this does on the 4052... Something
to try when I get home tonight, perhaps.

Joe, what was it you were saying about already having picked Rick's brains?

(FWIW I am still negotiating a trade with Zane for that ROM)

Now what we need are some exec calls for things like peek, poke, reading the
joystick port without a "pointer" instruction, and so on. I must step up the
pace of my own research...

Philip.
Received on Wed Feb 24 1999 - 11:22:38 GMT