hi,
If you want to set any 8 bits from 255 combinations, I cannot see a simple solution.

If you can accept, setting the state of the individual bits within an 8 bit byte from a possible 32 bytes, this is possible.

I know that you are only concerned with about 100+ bits, but the explanation
is the same, ie for 128bits, its 16 bytes, each of 8 bits.

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Yes Eric,
I also see that it could not be a simple solution now. I want to set ANY BITS from possible bits. If I have 8 bits then I want to have the capability to set any of them. The same if explanation, 100 + pins, then I could set any group of pins, (i.e. set 1 of them / or set 100 of them / or set 30 of them / or any thing...)
Even if I do not use simple logic IC, is there a possible solution? For example, could I use 8255 or Max307

 

hi,
The 8255 PIO is an old device, it has 3 * bit parallel I/O ports, only PORTC is bit direction addressable.
The MAX307 is the same logic as the HEF4067.

I cannot see an easy way to enable your parallel port to address any 8 bit combination from 128 or 256.
With above devices you will still have to work with defined 8 bit bytes.
That is, an 8 bit byte, having its bits updated in one write operation.

You should consider the speed/rate which an 8 bit byte from any 16 bytes can be changed via the port.
I estimate you could modify every bit of 128 bits within 1 to 2mSec, using the fixed byte method.

Question, when you ground the individual bits [output] of the 100+ outputs, what does the change do?

EDIT: added direction

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Each output will be connected to one pin of a device. The other pin of the device connected to the ground already. Then, if the output is High, these two pins have different voltage, meaning they are separated from each other. But when the output is Low (= ground) they have the same voltage (=ground) and connected. This action has the same meaning as short circuit. Changing the output from High to Low like switching OFF to On. If I have the ability to choose any pin H or L then I can switch On/Off each device freely !

And this switching on the devices need to be parallelly. 1 to 2 m Sec between them could be too long.

Any way could help me please ?

 

You are not selecting a single pin with the 74LS138, you selecting an octal latched buffer, 8 bits wide.

Action:
Address the 1st octal latch via the 138's
Write data byte to octal latch [could be 10010001]

Address another octal latch via the 138's
Write a byte to the selected octal latch. [could be 01101110]

And so on................

Got the idea?

You have told me about the output pin levels, but whats the end result?

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The result is switch the my devices ON/OFF .

 

I checked. The store has 74AC573 ICs. Use them with 74LS138 ICs could satisfy my application !?

What do you mean by addressing in the sentence :""Address the 1st octal latch via the 138's" ?

 

If I am going to give you my best answer for your problem, you must give me some feedback on my questions.

What devices are the 'bit' outputs switching??????

Whats the purpose of the selection???

74573 would work as the octal latches.

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Eric
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The device is a camera. Pushing the button to take snapshot means closing a contact of two wires. One wire I connect to the ground. The other to the output pin. If output Low, it will equal to ground and the camera shutters. So, if many camera take snapshot at the same time, requires many outputs.

I could think about the 74595 ICs. It is better than 74573 since it output does not change until having Enable signal. However it requires clock signal.

Do you know any IC that we input the data than stored it there. After that we input the second IC, stored it there, etc.. until input for all ICs. Then have a signal enable to all to get all the parallel output ?

 

The 74595 is a 8 bit serial inp/parallel output Shift Register.

>> Do you know any IC that we input the data than stored it there. After that we input the second IC, stored it there, etc.. until input for all ICs. Then have a signal enable to all to get all the parallel output ?

The 74373 octal latch has 3 state outputs.

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It is the same as 74AC573. When G is enable the data output follows the data input. That will not suit the application. The data need to be store somewhere in the IC, and only output when we control. So, we have IC 1 store the data, its recent output is all Low; the same for all other ICs. Only when we send "enable" then all of them output their private data at the same time.

The octal latch seems not to have this capability.

 

hi Nobita,
You are not taking the trouble to read the datasheets correctly or the drawings I have posted.

Good Luck.

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hi Nobita,
Lets give it one more try.

Refer and study attached drawing.

The 'NOR' gates can be replaced with simple invertors, Ive used NOR's to give an extra option in your control lines.

Ask me specific questions if you don't understand.

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Yes, I got the idea !

According to the drawing, I don't think only 8 pins of parallel port is enough for controlling. Example: Enable output, Enable selected latch, etc., while all these 8 pins of the port are also needed for the input data ?

 

hi,
Look at the printer port pin allocation and you will see that there are more than 8 ouput pins.

From memory there are 4 more output pins and 4 input pins.

I will search my data base an attach as an EDIT.

Done: Please read.

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