Recent questions on the 74 and 84 from a programming point of view have
prompted me to repost the response to two messages that were written by
Jim Robertson of Newfound Electronics.

Jim currently isn't on the PICLIST, but has reasonable experience with
these
devices, as he is the designer of the Warp-3, PP1, and Warp-17
programmers.

======================================================================
74 and 74A

At 10:28 AM 1/10/97 GMT+1100, you wrote:
>I am 3/4 way through a program which uses a PIC'74. Also I have
>working code on other 74's. I now need to program more of these
>devices but I think the 74 has turned into a 74'A' which is slightly
>different from the original.
>I downloaded the data sheet for this chip but at 350 + pages I am
>sure to miss something.
>My question is - will the 74'A' devices program in a programmer
>designed for the original 74?
>
>Thanks for any help.
>
>Best regards for the new year
>Tony
>
Tony,

Do this:

Reverse the PWRTE bit, if you want it "ON" select it as "OFF" and vice
versa.

Do not code protect the 16C74A! You will not be able to erase the code
protection bits if you do.

The Brownout will not be available on you "A" part. It will (should!) be
turned "OFF" by default by your programmer.

There are extra code protect bits in the "A" part but as you are not
programming them they do not matter.

All the other config bits, ID etc are the same!

Just remember to not code protect the "A" part and you should be ok.

Jim

=================================================================
C84 and F84

At 09:48 AM 1/16/97 -0500, you wrote:
>Please excuse my confusion. What is the difference between the
>EEPROM 16C84 and the FLASH 16F84? I know the 'F has more RAM bytes,
>but aside from this, what's the practical difference? Is there
>any difference in programming, number of write cycles, etc?
>
>-Tony

16F84 has PWRTE bit reversed (like ALL newer parts) when compared to the
16C84. All the spare config word bits in the 16F84 are used for code
protection. The effect of code protecting a 16F84 is different from a
16C84.

(If you want to know the esoterica of it all download the programming
specs
form the microchip web page but it usually is of little interest  to the
"man in the street.")

Programming wise, you can program the 16F84 as a 16C84. Remember to
reverse
the code protect bit and don't expect code protection to be the same.

Jim

==============================================================

Don McKenzie  don@dontronics.com   http://www.dontronics.com

SLI, the serial LCD that auto detects baud rates from 100 to 125K bps.
SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
Covers all versions of the PIC16cxx family plus the Atmel AT89C2051.