Which PIC to use?

This Forum is about the Opentherm gateway (OTGW) from Schelte

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MrHidden
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Which PIC to use?

Post by MrHidden »

Hey there,
Now two kinds of PIC's are used, the P16F88 and the P16F1847, when i read the online documentation the P16F88 is preferred.
But in another part of the website, I see that the P16F1847 is the one most updated.

I have both but which one do I have to use to get the most benefits?

Anyone with information about that subject?

MR
hvxl
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Re: Which PIC to use?

Post by hvxl »

Which part of the documentation gives you the impression that the P16F88 is preferred?

The PIC16F1847 has more memory (both code and ram), has more capabilities, works over a bigger voltage range, is cheaper, and normally has a shorter lead time.

With the latest gateway firmware, the PIC16F88 has exactly 1 free code word left, while the PIC16F1847 already has more features using only 53% of its code space. In case it's not clear, there is not a whole lot that can be done in 1 code word. So, when you have the choice, I would definitely suggest to go for the PIC16F1847.
Schelte
MrHidden
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Re: Which PIC to use?

Post by MrHidden »

The website tells at point DIY gateway: http://otgw.tclcode.com/index.html#gateway

The circuit is designed around a PIC16F88. Due to chip shortages in early 2022, the PIC16F88 was difficult to obtain. For that reason a version of the firmware has been made for a PIC16F1847. The two PICs are pin-compatible. The features of the PICs are used in such a way that no code is needed to forward messages from the thermostat to the boiler and vice versa in monitor mode. However, with the appropriate firmware, the device is also able to create and send any desired message."

I read at that sentence that the PIC16F88 is the "good" one and the PIC16F1847 was used due to chip shortage.

Or do I miss something?

Mark
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hvxl
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Re: Which PIC to use?

Post by hvxl »

The chip shortage was the motivation to look for a replacement for the PIC16F88. The first idea was to switch to a PIC16F18426, but that only has 14 pins instead of the 18 of the PIC16F88. So it would require a new PCB layout. After more searching, I stumbled across the PIC16F1847, which allows different pin configurations for the serial interface. In one configuration it is pin-compatible with the PIC16F88, while in another configuration it is even pin-compatible with the PIC16F627 and PIC16F628 that I used for the original prototype. The memory of the PIC16F88 was nearly filled to the brim. So it was very fortunate to find a compatible chip with more resources. The only down-side was that the code had to be extensively reworked to run in the new PIC.

I'll update the description on the web site.
Schelte
MrHidden
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Re: Which PIC to use?

Post by MrHidden »

Thank you,

And you already updated the WEB page.

The gateway is working great here, I found some interesting things about my Intergaz boiler since i started to use the OTGW.

And my energy bill is getting lower and lower.

Keep up the excellent work,

Mark
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