# information

#### islam

Joined Nov 29, 2005
4
i want to interface between computer &device of those devices
"82C55 : programmble prepheral interface"
"steeper motor"
"8279 : programmble keyboard / display interface"
what is the advantage of connecting these devices to computer?

#### Murod

Joined Dec 24, 2005
30
Originally posted by islam@Dec 5 2005, 11:20 AM
i want to interface between computer &device of those devices
"82C55 : programmble prepheral interface"
"steeper motor"
"8279 : programmble keyboard / display interface"
what is the advantage of connecting these devices to computer?
[post=12198]Quoted post[/post]​
The advantages is the reason why You want to interface that devices.

#### peajay

Joined Dec 10, 2005
67
> "82C55 : programmble prepheral interface"

Unless you need a specific feature of the 82C55, and you probably don't, forget about it. It's both simpler and cheaper to use things like the 74LS373 for outputs and the 74LS244 for inputs. Each is about $0.45, whereas the 82C55 is$4.50. (there may be better selections in CMOS, but I don't know anything about those)

> "steeper motor"

Stepper motors blow. They require an insane amout of power, they're not very strong, and if you want them to be the least bit accurate you've got to run them really slowly. Use some kind of servo setup instead.

> "8279 : programmble keyboard / display interface"

Oh no...

> what is the advantage of connecting these devices to computer?

Well, the PPI, or more cheaply the TTL chips I spoke of, would provide convienent and simple to use I/O ports on an otherwise overcomplicated to the point of being essentially useless for any fun electronics project PC. I once had an ISA card that I built with a PPI on it, and the 24 I/O lines shoved through a 25-pin DIN connector on the back. It was loads of fun until one day it broke my computer somehow. (I don't remember exactly what the problem was, but I seem to remember doing something stupid like putting it in without all of it's chips in their sockets.) Were I feeling brave enough, I'd certainly make another, as the single ISA slot in my computer is no longer in use, but this time I'd use two 74LS373s and a single 74LS244 instead. That would make 8 bits of input, 8 bits of output, and 8 bits for the PC to control external circuitry so as to multiplex that into even more bits if necessary.

Stepper motors are some fun. I once built a CNC mill with some stepper motors controlled by my PC via the parallel port. I wanted to use it to mill out printed circuit boards, but it ultimately turned out that the Dremmel I was using wobbled around too much, the tiny drill bits were way too flexible, and the stepper motors sucked a bit too much as they ended up skipping steps if met with even the slightlest bit of opposing force. (and the thing was scaled down to 2000 steps per inch, so it's not like the things were being asked to do all that much work) I thought up solutions to all of those problems, I found better drills, drill bits that are only tiny and flexible at the tip, and certainly a servo system would do way better for speed and accuracy, but I didn't have the money for any of that, in particular it seems that even plastic gears contain ingredients like diamonds or gold or something that makes them horridiously expensive. So instead I just disassembled the thing and tossed it in the trash so that I could reclaim the much more valulable 4 sq. ft. of space it was consuming in my apartment. Even though every hole it drilled was in slightly the wrong place, and after running for three hours (yes, I said stepper motors are slow) it was half an inch from where it was supposed to be, it was still pretty cool. Just not the least bit useful.

As for the 8279, I wouldn't mess with it. It's pretty expensive at $12.99 for a used one, and the only time I've needed display/keyboard scanning abilities were when I was working on my Z80 computer project, and then it was simple enough just to make the Z80 itself do all of the scanning via an interrupt. The Z80 can be had for$4, 32k of SRAM can be had for $2, and 256k of flash is only$3.70, or less if you're willing to play with surface mount components. So I'd just use another Z80 instead if I had to.