BS2p-24 I/O pins requirements and 74xx families.

Archiver

Ciao,

I'm sure that the problem has been discussed a lot af times... But it's not so
friendly to me the matter about I/O pins current requirements of the BS2p-24
that I'm trying to put inside my circuit, therefore I ask your help, dear
friends, before I may cook my precious Stamp!

First thing: a simple rule for establishing the fan-out (and fan-in) of the
Stamp's I/O pins?

Second: what is the best choice about the logic family to interface with the
Stamp? 74HC, 74LS or what else?

Last: are the two I2C ports of the BS2p-24 (and BS2p-40) limited to a certain
number of I2C devices connected to the same bus?

Thanks in advance,

Alberto.


[noparse][[/noparse]Non-text portions of this message have been removed]

Archiver

I believe the lowest power, yet still TTL family,
is 74HCT. Some of the HCx family are NOT TTL
compatible, so be careful.

The BS2 can source or sink 23 mA max per pin,
with a max for all pins of 50 mA.
(Which means: 2 pins at 23 mA, or 16 pins
at 3.125 mA each, etc). Note it
seems to 'sink' better than it 'sources',
if that matters to you.

If you need more current, the 74HCT595 is
a very good SPI to parallel converter, with
more total power available.

For Fan-Out, you need to find the input
resistance of the chips you want the BS2
to drive. For Fan-In, I believe the BS2's
inputs look like 10 Meg-ohm impedances --
someone may correct me on that.

The big problem with BS2 is that because
it can drive so much current, if you tie
two drivers together and have them drive
in opposite directions, with no resistance
between them, it is easy to burn out a pin.

The brute-force solution to this
problem is to put a 220 ohm
resistor in series with each pin which might
be tied to another driver. This will guarantee
that the current won't exceed 22mA, no matter
what states are active.

I2C I don't know the answer to that one.

--- In basicstamps@yahoogroups.com, "Alberto Calderara"
<albertocalderara@t...> wrote:
> Ciao,
>
> I'm sure that the problem has been discussed a lot af times... But
it's not so friendly to me the matter about I/O pins current
requirements of the BS2p-24 that I'm trying to put inside my circuit,
therefore I ask your help, dear friends, before I may cook my
precious Stamp!
>
> First thing: a simple rule for establishing the fan-out (and fan-
in) of the Stamp's I/O pins?
>
> Second: what is the best choice about the logic family to interface
with the Stamp? 74HC, 74LS or what else?
>
> Last: are the two I2C ports of the BS2p-24 (and BS2p-40) limited to
a certain number of I2C devices connected to the same bus?
>
> Thanks in advance,
>
> Alberto.
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]