Before i apply this ckt to my laptop...

[ikalogic]

hello,

Before i apply this ckt to my laptop... i just wanna make sure everything is ok.

it is an ISP programmer for the AT89S52.

it will be connected to the // port of my laptop.

I am using AND gates as buffer (just because i don't have a dedicated buffer IC right now, and can't wait to get one)

just wanna make sure that my approach is correct. I know it is a VERYYYY simple circuit.. but.. as i told.. its my poor litle darling laptop we're talking about here! so, i m just waiting for a confirmation to build the ckt.

final note: if the laptop blows up killing me and the people living in my building, don't worry i won't blame anybody here for it!

 

[ikalogic]

oooooops forgot to tell you, the last gate is inverted w/ reguard to the others, because this last one is to buffer an input (rather than an output like the others...)

 

[audioguru]

It is an old TTL gate. Its minimum output high voltage is only 2.7V and won't drive Cmos without a pullup resistor. Its output current is low but OK for logic.

 

[ikalogic]

But it will be used to to control I/O pins of a TTL mircocontroller... i don't think we need more current. do we?

thx

 

[kchriste]

Before i apply this ckt to my laptop... i just wanna make sure everything is ok.

It looks OK. About the only thing that you could do to ruin the port would be to apply power backwards to the circuit or maybe apply 12V instead of the 5V. Power it up first when it is not connected to the laptop and make sure that all voltages relative to ground (pins 18-25) are between 0 & 5V on pins 6,7,8 & 10 and you should be safe.

It is an old TTL gate.

But it's not a vacuum tube!

 

[audioguru]

The filament in an old TTL gate (compactron?) eats power and makes the IC warm. Hee, hee.
I would use a 74HC08 which is Cmos with a very low supply current, an output that goes to +5V and to 0V and has 25mA source or sink current. The same as in microcontrollers.

 

[Sceadwian]

Over current resistors aren't going to hurt.

 

[ikalogic]

Over current resistors aren't going to hurt.

thanks, but.. which value to use... i guess 470 would be suitable? or maybe 220 ?

 

[audioguru]

If you ever want to drive old 74xx TTL logic or LEDs, then use 120 ohms.

 

[ikalogic]

hello, thanks guys, by the way i just made the ISP programmer to work...

but i was really unlucky, i passed through all the bugs one can pass through when building this circuit , e.g.:
-Too long cables
-Noise,
- 2 defectious AT89S52 chips,
-Parallel port configuration (EPP, SPP..)

Anyway, just letting you know guys, if anyone is in trouble building his ISP, i may help!

 

[ikalogic]

my ISP programming cable is done:

**broken link removed**

I wouldn't bother saying, i hate to be anoying! but i know some guys here like to see the results of the projects dicussed in the forum..

 

[Hero999]

The filament in an old TTL gate (compactron?) eats power and makes the IC warm. Hee, hee.

I can't believe these things were made up until the early 1990s
https://en.wikipedia.org/wiki/Compactron