From: Segher Boessenkool <>
Date: Tue, 26 Jul 2016 03:08:56 -0500
Message-ID: <>
On Tue, Jul 26, 2016 at 08:22:46AM +0200, wrote:
> > I believe the MOS hardware manual introduced the name RDY, but it also
> > directly compared it to the HALT on the 6800 (chapter 1.2.1, p. 12, on
> > Hardware Manual from Janury 1976, 2nd edition, Revision A,
> >

6501 is plug-in compatible to 6800, on most designs.

> 6800                              6501
> Halt - Stops processor [...]      Ready - Stops Processor [...]
> The only reason I can think of is that they wanted to somehow differentiate from how 6800 handles the signal (after completing the current instruction) as opposed to how 65xx does,

There are more differences -- for example, RDY does nothing during writes,
so RDY will only do anything at the *next* insn if you enable it at a write

> but the choice of the name still seems like an unfortunate one for me.

As is explained in this manual, the pin should be set high when the slow
rom you are reading is READY :-)

From the chip layout it is obvious the earlier 6500 designs did not have
RDY at all, btw.


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