UniBone Successful test and I2C Panel question: Inline L or R

[Jay Jaeger]

I now have a memory test running on my Unibone - a 128K board from Cambex, only needs +5V.  (I tried some Plessey boards that use +5 / +15, but apparently they were not working.)

So, on to the I2C panel.  

Firstly, in looking at the board and schematic I see some notations that are not clear to me, for R6, R7 and R8 (10, 10 and 1K ohms, respectively).   On the board silkscreen, I see "L or R" and the schematic reads "Inline: L or R".  What does that signify?

Also, for R3, the silkscreen reads 1K, but the schematic says "R3: > 1K, voltage divider with 220 on UniBone" with a 10K resistor.

???

JRJ

[Joerg Hoppe]

Jay,

> So, on to the I2C panel.
>
> Firstly, in looking at the board and schematic I see some notations that
> are not clear to me, for R6, R7 and R8 (10, 10 and 1K ohms, respectively).

Panels are planned to cascade, and I wasn't sure how I2C behaves in
possibly noisy environment.
R6 + R7 are part of an optional spike filter, to have a point to insert
ferrites or a RC lowpass.
Use 0-ohm wires.

R8 could protect the MCP23017 Reset line ... use anything between 0 and 1K.

> Also, for R3, the silkscreen reads 1K, but the schematic says "R3: > 1K,
> voltage divider with 220 on UniBone" with a 10K resistor.

R3 is a terminator for Reset. Should be only placed on the last panel in
a daisy chain, like the SDA and SDL terminators.
It works against a 220 Ohm pullup, so should not be smaller than 1K .

All these resistors are not critical for a single panel with short cable.

> On the board silkscreen, I see "L or R" and the schematic reads "Inline: L
> or R". What does that signify?

OK, confusing.
I talk  of a "Left" and "Right" input line here, but it should be:
"There is an I2C IN and an I2C OUT pin header, but these are really
interchangeable."

kind regards,

Joerg

[Jay Jaeger]

Or, maybe,  L == inductor  R== resistor ??

Thanks.

[Joerg Hoppe]

Am 15.09.2022 um 17:34 schrieb Jay Jaeger:
> Or, maybe, L == inductor R== resistor ??

Hey, thats a much better explanation!

Joerg