In comp.sys.raspberry-pi, you wrote:
>> {Wow -- those 2x16 LCDs have mutated since I last looked at them...
>> I think I have one or two of the pure 8/4-bit parallel models
>
> Thats the model I was referring to (salvaged a number of them).
>
> The "I2C backpack" is actually just a dumb 8-bit I2C expander plus a
> backlight-feeding transistor and a potmeter for the contrast.  In short,
> everything you normally feed to the 4-bit interface of the LCD now has
to go
> over I2C - hence the previously mentioned checking of the LCD's busy
line.

I've made my own backpack for a 4x20 LCD using an MCP23017. Works fine. I
didn't bother with monitoring the busy flag. There are various timing
tables for HD44780 operations in the data sheet which can be used. Makes
it a lot simpler, and you would generate a hell of a lot of I2C traffic.
I've also programmed HD44780 character LCDs direct as well, without using
the busy flag - it is a very common prectice. I belive all the HD44780
look-a-likes maintain the timings.

Jim

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