More IO Pins
I've been thinking about different ways to expand the number of IO
pins on a bs2, and came up with an M54HC595 and a M54HC597. The
chips are made by ST, and cost about 50 cents. The 595 converts
serial data into parallel, while the 597 converts parallel to
serial.
The basic idea is that through using Serout, you send 8 bits out of 1
pin, and the 595 separates them so you get 8 separate pins. The 597
is the exact opposite, changing 8 parallel bits into 8 serial ones,
so you can read in 8 values off of one pin.
The chips need 3 IO pins off the STAMP to run, but provides you with
8 extra ones, so if you use 4 chips, you could have 16 inputs, 16
outputs and 4 original pins leftover.
The only problem with this is that the new IO's are not
bidirectional, the only way you can change a pin from an output to an
input or back is to swap the chips, which isn't very practical.
Anyone know of any converters that can go both ways? Converting
serial to parallel AND parallel to serial?
-Chris
pins on a bs2, and came up with an M54HC595 and a M54HC597. The
chips are made by ST, and cost about 50 cents. The 595 converts
serial data into parallel, while the 597 converts parallel to
serial.
The basic idea is that through using Serout, you send 8 bits out of 1
pin, and the 595 separates them so you get 8 separate pins. The 597
is the exact opposite, changing 8 parallel bits into 8 serial ones,
so you can read in 8 values off of one pin.
The chips need 3 IO pins off the STAMP to run, but provides you with
8 extra ones, so if you use 4 chips, you could have 16 inputs, 16
outputs and 4 original pins leftover.
The only problem with this is that the new IO's are not
bidirectional, the only way you can change a pin from an output to an
input or back is to swap the chips, which isn't very practical.
Anyone know of any converters that can go both ways? Converting
serial to parallel AND parallel to serial?
-Chris
Comments
>I've been thinking about different ways to expand the number of IO
>pins on a bs2, and came up with an M54HC595 and a M54HC597. The
>chips are made by ST, and cost about 50 cents. The 595 converts
>serial data into parallel, while the 597 converts parallel to
>serial.
>
>The basic idea is that through using Serout, you send 8 bits out of 1
>pin, and the 595 separates them so you get 8 separate pins. The 597
>is the exact opposite, changing 8 parallel bits into 8 serial ones,
>so you can read in 8 values off of one pin.
>
>The chips need 3 IO pins off the STAMP to run, but provides you with
>8 extra ones, so if you use 4 chips, you could have 16 inputs, 16
>outputs and 4 original pins leftover.
>
>The only problem with this is that the new IO's are not
>bidirectional, the only way you can change a pin from an output to an
>input or back is to swap the chips, which isn't very practical.
>Anyone know of any converters that can go both ways? Converting
>serial to parallel AND parallel to serial?
All PICS - from which the Stamp was born !
>
>-Chris
>
>
>
>
>
Sounds as if you're looking for an I/O coprocessor... Try here:
http://www.al-williams.com/awce/pak3.htm
>I've been thinking about different ways to expand the number of IO
>pins on a bs2, and came up with an M54HC595 and a M54HC597. The
>chips are made by ST, and cost about 50 cents. The 595 converts
>serial data into parallel, while the 597 converts parallel to
>serial.
>
>The only problem with this is that the new IO's are not
>bidirectional, the only way you can change a pin from an output to an
>input or back is to swap the chips, which isn't very practical.
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
Sounds like a nice chip, but the price really isn't worth it. The 8
bit SIPOs and PISOs are only about $0.50, while these cost $25.00. I
think I'll stick with what i have for now, but thanks anyway.
-Chris
output, a shift register is much less expensive. However the PAK-III and IV
do all the usual I/O operations independent of the Stamp (PWM, Sound, etc.).
So I wouldn't characterize it as "not worth it" any more than I would say a
PC is not worth $500 because I can get a Stamp for $50.
No offence taken or hopefully given, but I did want to go on record for
that.
Regards,
Al Williams
AWC
* Expand your Stamp's I/O with a PAK-III or PAK-IV:
http://www.al-williams.com/awce/pak3.htm
>
Original Message
> From: Chris [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=8-W4RbQ-m9gUgwa1PniS04iuL3j6AmMkeKZH7YlRef6hHqDDVxd-R3BNR2zjuO8nfIiYGvQCTVnHZhj8cw]c_rosney@y...[/url
> Sent: Friday, April 21, 2000 5:01 PM
> To: basicstamps@egroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] More IO Pins
>
>
> Mike,
>
> Sounds like a nice chip, but the price really isn't worth it. The 8
> bit SIPOs and PISOs are only about $0.50, while these cost $25.00. I
> think I'll stick with what i have for now, but thanks anyway.
>
> -Chris
>
>
>
> ...The 595 converts serial data into parallel, while the
> 597 converts parallel to serial...
> ... snip
> The only problem with this is that the new IO's are not
> bidirectional, the only way you can change a pin from an output to an
> input or back is to swap the chips, which isn't very practical.
> Anyone know of any converters that can go both ways? Converting
> serial to parallel AND parallel to serial?
You don't necessarily have to swap the chips. You can tie the 8 outputs
from the 74HC595 together with the 8 inputs to the 74HC597. The '595 is
tristate--Bringing its pin (13) high disconnects the outputs from the pins,
and whatever you have connected externally can at that point be latched
into the '597. (Some resistors might be a good idea for contention
protection.) It does take a lot more pins on the stamp than the "smart"
i/o expanders that are based on the PIC chip.
> basic idea is that through using Serout..
Typo?.. That should be Shiftout. The "smart" chips use serout, and take
fewer pins on the stamp.
-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
Hey, no problem. It's just that what you're talking about is way
more sophisticated than i really need, so for me, it isn't really
worth buying.
-Chris
Thanks, that's a great idea. I wish I would have thought of that.
And yes that was a typo. I was thinking serial and parallel so i
typed Serout instead ouf Shiftout by accident.
-Chris