PIC16C745 vs ?

Ramey · Guest

We are making a custom usb keyboard and it seems that the PIC16C745 is ideal for this. We've been very happy with Microchip and CCS products so far. CCS contains an coupe of USB examples so it seems to me its perfect for us. But I do have one concern.

It seems that this chip is sort of "out of favor" compared to the newer - "high speed" alternatives. Is there any reason we should be using the newer version rather than the one that seems perfect as is?

Robert Ramey

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

You didn't mention why this chip is perfect for your application so we can only give some general hints.

With Microchip the newer chips are manufactured with newer technology, giving you more features for the same or less money.

There are only two USB PICs in the PIC16 series, all others are from the PIC18 series. PIC18 processors are more powerfull but this is probably not very important to your application. Still I do prefer the PIC18 because RAM on the PIC16 is tiny. And the PIC18 has lots of other small improvements so you don't waste a lot of time to work around the PIC16 'features', for example a latch on the I/O pins to name one thing.

The letter 'C' denotes a One Time Programmable chip (OTP). Unless you are really sure you never have to do a firmware update I would go for one of the 'F' types which can be reprogrammed in-circuit (implement a bootloader).

Check prices and availability before you make a final decision. Some models are more common than others.

At 25 pieces from Digikey.com:
PIC16C745 USD2.97
PIC18F2450 USD3.75

According to the Microchip website the new PIC18F65J50 is the same price as the 18F2450 but with double the memory and 64pins instead of 28 pins. Not avaiable yet through Digikey and I'm always afraid of new designs with their unknown errata.

Guest · Posted: Thu Aug 30, 2007 5:49 pm

its perfect because it had everything I needed and (almost) nothing I didn't. Also it uses the 16x instruction set that I'm familiar with. If I use the 18x I have to get the CCS PCH compiler. I was also a little concerned that the microchp website doesn't show a keyboard example and they recommend some other compiler. This is a simple ap, I'm fine with OTP but the first units will be socketed - just in case. Oh about $1 cheaper, though this isn't a big consideration here. I notice that the CCS compiler example, handles the either PIC. I'm curious where the actual USB library code is found.

Anyway,

Thanks for the observations.

RObert Ramey