16LF877A at 20MHz?

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Can you run the 16LF877A at 20MHz? My supplier (Farnell) lists the LF as 20MHz compatible. I’ve used the A before and the LF was the only one in stock so I happily bought and soldered in!

I can’t get it running.

On looking at the 16F877 datasheet the little info on the LF seems to list DC to 4MHz at 5v operating while the -A LF goes DC to 10MHz.

The LF devices don’t have a helpful speed indicator their part number. I Have a PIC16LF877A-I/PT for instance

I wish microchip would distinguish between the LF and F on their front sales spec page without picking and choosing the best specs to put in!

A simple table listing the difference between the LF / A / and extended versions would be nice!

Can anyone confirm this (I am getting paranoid now!) before I phone Farnell and get them to change their catalogue!

Will

drh · Posted: Wed Sep 22, 2004 7:42 am

Maximum frequency for the 16LF877A is 10Mhz.
Datasheet DS39582B, page 174, Fig. 17-2.
_________________
David

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Both RS comonents and Farnell incorrectly list the LF as running at 20MHz. Must be duff infomation from Microchip to the suppliers! How many times have I not double checked everything with the datasheet! This will hopfully be the last!
Thanks, and keep well,

Will

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

adamwynne · Guest

I have a spare 40pin and 44PLCC in the 'F' 20Mhz if you are short one.

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

You are kind. It was a TQFP device as it happened which is doubly annoying as they are a pain to de-solder I usually use PLCC now but amazingly the mechanical designer only gave me a 3mm height clearance from the surface of the PCB so it’s my first time with the TQFP ones!

In the end I snipped its little pins off and unsoldered each pin separately. I found a 16F877 in the correct package in a “samples” order I received from Microchip last year and never used so was quite happy, until of course I soldered it in and it exhibited the same behaviour as the LF part with the 20MHz crystal (a small surface mount device which would have been even worse to remove than the PIC and just as expensive would you believe!).

Anyway after a coffee and a head scratch I realised my mistake was that I hadn’t programmed them! I forgot that from the factory they (PICs) come LVP enabled and as I had left B3(PGM) floating the oscillator was switched off as the PIC was in programming mode!

A quick program later and I was up and running.

All worked out for the best as if that LF part had oscillated OK at 20MHz I would have probably specked that for the production run.

Anyway have a good weekend guys,

Will

Guest · Posted: Mon Sep 27, 2004 4:38 pm

Sorry to point this out, but the 16F877 is spec'd @ 20Mhz at 5V and it NOT guaranteed to run at 3V. (though most do work at 3V, but not at 20Mhz !!!)
The 16LF877 is spec'd @ 10Mhz at 3V.
Speak from bitter experience......