[A83] Re: LD A,R ; LD R,A

To: assembly-83@lists.ticalc.org
Subject: [A83] Re: LD A,R ; LD R,A
From: ComAsYuAre@aol.com
Date: Sat, 14 Jul 2001 10:14:44 EDT
Reply-To: assembly-83@lists.ticalc.org

>From "Programming the Z80" by Rodnay Zaks:

"The R register is the memory-refresh register.  It is provided to refresh 
dynamic memories automatically.  Such a register has traditionally been 
located outside the microprocessor, since it is associated with the dynamic 
memory.  It is a convenient feature which minimizes the amount of external 
hardware for some types of dynamic memories."

Basically, the r register gets incremented each byte of instruction code.  
It's used in some pseudo-random number generators, such as ztetris, but it 
can't be used without some sort of variable-length delay between uses (such 
as waiting for someone to hit a key), because otherwise the output won't be 
very random.  Otherwise, it has little practical use on calculators.

In a message dated 7/14/2001 2:44:27 AM Eastern Daylight Time, 
hyper@hysoft-automation.com writes:

> 
> When using the tasm80.tab file, I 
> came upon the opcodes LD A,R and LD R,A
> They have a '1' at the end of the line 
> (the class), so I guess they're four our 
> processor. But I'm curious as to that this
> R means. It can't be meaning 'other registers' 
> since they're all taken care for elsewhere in the
> table file. My guess is that it's a special system 
> 

----
Jonah Cohen
<ComAsYuAre@aol.com>
http://jonah.ticalc.org

Follow-Ups:

[A83] Re: LD A,R ; LD R,A

From: "Michael Vincent" <hookman@worldnet.att.net>