From: ervin@pinbot.enet.dec.com (Joseph James Ervin)
Subject: Re: Some questions ....
Reply-To: ervin@pinbot.enet.dec.com (Joseph James Ervin)
Organization: Digital Equipment Corporation
Date: Mon, 17 Aug 1992 12:21:25 GMT


In article <199208142309.AA06118@seq.uncwil.edu>, P5JARGOM@UTFSM.BITNET (Javier Argomedo Zazzali) writes:

|>Hi,
|>I'll be very grettigs if anybody can answer some questions about
|>my hp48s.
|>
|>* What really does the ML RESET instruction...? i read that it
|>reset the data bus (or something alike), but when i dissasemble
|>the ROM (at @00000 address or at @0000F for interrupts) there are
|>some branchs that does a RESET  ???

The reset instruction essentially just sends "reset" command onto the 
I/O bus inside the HP48.  It does not reset the CPU; instruction 
execution proceeds normally and the CPU registers are not modified by 
the RESET instruction.  The various portions of the HP48 hardware
other than the actual CPU (for example, the mem controller, 
the display controller, any installed ROM cards, the serial
line controller) are all I/O devices that sit on the CPU's 
bus.  The RESET instruction resets _those_ devices, i.e.
all of those devices are "unconfigured" and will no longer 
respond to their addresses until they are reconfigured.


|>* Have anybody the descriptions of the Operating System Flags
|>lacated at @70XXX?, some of them are documented in the internals
|>listings, but are only a fews ones....

|>* Have anybody the descriptions of the hardware IO registers located
|>at @001XX  ??? they are used in the interrupt handling.

Let me send you my disassembly of the interrupt handler. It should 
answer many of the questions you have.

|>* I don't remember where,but i had read a document that says that the R4
|>register was used as a interrupt vector, and it cannot be changed,

This is false.  Interrupts do not alter the contents of any of the 
CPU registers.  

|>Wich is exactly the function of the r4 register  ???  is rigth my
|>information ?

R4 is a normal register just like R0-R3.  No difference.

|>* I had open my 48s, and i found that it have some type of connector
|>on the back side of the printed circuit...  i think it is the
|>connector to the expansion ports ...  I want to add some tipe of
|>IO to my calculator,  Have anybody the descrptions of that signal
|>lines ??   refered to the ones of the memory pack.

Good luck.  Maybe you should have bought the HP48SX, eh?

|>
|>Thanks a lot...
|>
|>ps.    excuse my pooooooooor english.
|>
|>=========================================================================
|>Javier Argomedo Zazzali                      e-mail P5JARGOM@UTFSM.BITNET
|>Electronic Engineering Student
|>UTFSM University, Valparaiso, Chile.
|>=========================================================================
|>


I'll try to send along my disassembly of the interrupt handler, but
if you don't hear from me in a day or so, then please send mail to 
"ervin@pinbot.enet.dec.com".

Also, any other ML programmers out there who would like to know 
more about how the I/O hardware on the HP48 works, send me mail
and I'll forward you a copy as well.

Regards,

>>>Joe Ervin
Newsgroups: comp.sys.hp48