Wanted: ASM-48 for Intellec MDS-2

Mike Stein mhs.stein at gmail.com
Thu May 21 11:46:22 CDT 2015


I think I got confused between the CPU reading
external memory and reading its internal memory
from the outside; also I must have misremembered 
how I'd read one in my distant youth.


----- Original Message ----- 
From: "Eric Smith" <spacewar at gmail.com>
To: "General Discussion: On-Topic Posts"
<cctech at classiccmp.org>
Sent: Wednesday, May 20, 2015 7:16 PM
Subject: Re: Wanted: ASM-48 for Intellec MDS-2

> On Tue, May 19, 2015 at 11:28 PM, Mike Stein
> <mhs.stein at gmail.com> wrote:
>> My 8041A/8641A/8741A data sheet says
>> "interchangeable ROM and EPROM Versions",
>> "Single
>> 5V Supply" and "Vdd (Power): 5V during normal
>> operation".
> "Normal operation" is the key phrase. ROM (or
> EPROM) verification mode
> is not considered "normal operation".  In normal
> operation, the
> 8041A/8641A/8741A is executing the ROM/EPROM
> code, and you can apply
> an address externally to the port pins until the
> cows come home, but
> that won't make it dump the contents of that
> address.
>> I'm pretty sure I've read 8741s without any 25V
>> supply; AFAIK Verify mode is not the same as
>> Read ('normal') mode.
> This isn't a 2716. There isn't a "read (normal)"
> mode. Normal mode is
> executing code, and doesn't allow reading the
> ROM (or EPROM) contents
> externally.  Verification mode is the only mode
> that provides for
> external access to the ROM/EPROM contents. The
> only documented way the
> chip knows to be in verification mode is a
> supervoltage on the EA pin.
> A National Semiconductor app note suggests that
> 9V is adequate for
> reading their 804x masked ROM parts; they
> specifically mention
> internal circuitry that detects a voltage on EA
> above a certain
> threshold which puts the part into verification
> mode. The 9V National
> describes might or might not be adequate to read
> Intel masked ROM
> parts.  Intel specified 12V to read the 8048.
> Intel neglected to
> specify the supervoltage required for ROM
> verification mode for the
> 8041 and 8041A, but I'm pretty sure they
> expected 12V for those as
> well.

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