Xref: utzoo comp.sys.intel:514 sci.electronics:3728
Path: utzoo!attcan!uunet!mcvax!ukc!pyrltd!lucifer!rob
From: rob@lucifer.UUCP ( 237)
Newsgroups: comp.sys.intel,sci.electronics
Subject: Re: 8051 - 8751
Message-ID: <27@lucifer.UUCP>
Date: 31 Aug 88 09:07:20 GMT
References: <1988Aug27.180524.1964@gpu.utcs.toronto.edu> <1988Aug28.002342.16425@utzoo.uucp>
Reply-To: rob@lucifer.UUCP (Rob Clive)
Organization: Lucas Diesel Systems, Phoenix Way, Cirencester, Glos, UK  (0285 67981)
Lines: 42

In article <1988Aug28.002342.16425@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>
>They don't redesign the thing, of course, but they do pump your ROM data
>into a program that generates a custom mask for one layer [I think it's
>only one] of the ROM part of the chip.  That's why it's called "masked ROM".

Yes it is only one.  The 2000 piece minimum order sounds like a bargain;  for
"mature" processors (like 8051, 8048, 6801, etc.) the minimum order quantities
are rising because of the better yields being achieved and thus the lower unit
cost.

>it is reported that when you buy "ROMless" one-chip micros from Motorola, you
>are probably getting masked-ROM parts which turned out to have defects in
>the ROM area.

I heard this too but was informed that this poses a problem:  how do you ensure
that enough masked parts have defective ROMs to meet demand? :-)

>>[Intel says]	The windowless eprom part ... is only about $5.00 cheaper
>>... because plastic is not much cheaper than ceramic etc. etc..
>
>it is true that on-chip EPROMs
>are quite a bit harder to make than on-chip ROMs.

Not quite.  EPROM parts are more expensive in terms of chip area and
packaging required (ceramic or cerdip packages are not cheap) and they pose
design problems: how do you ensure complete emulation of the masked parts
AND add the extra circuitry to allow programming?  When first introduced
EPROMs were treated as a (low volume) necessary evil by the chip manufacturers
as a route to selling more ROMs.  Now of course some users never reach the
masked ROM stage and EPROMs are 'respectable'.  As to OTPs, well, the
difficulty here is testing; EPROMs are normally tested by programming test
patterns and then erasing before delivery which would not be very useful :-)
One method which (I think) is used is to have a small area of extra EPROM
which can be programmed as a test.  Of course all this costs money hence the
price.  Mind you, it doesn't cost THAT much; someone somewhere is making a
large profit thank you very much! :-)

----------
Rob Clive.					UUCP:	mcvax!ukc!lucifer!rob
Lucas Diesel Systems, Cirencester	 Most others:	rob%lucifer@ukc.ac.uk
Gloucestershire, GL7 1QG, UK.				      Now read on....