Can somebody explain this circuit?

[Zillolo]

Hello friends,

I was wondering if anybody could help me understanding this circuit. I dont understand how the part with the Tristate-Logic works.
Also what is the stuff in the lower right about?

Thanks, if anybody can help me

SN74AC245N : http://pdf.datasheetcatalog.com/datasheet2/2/04s23w7ofajcr2cwwiz11icct2wy.pdf

[N2IXK]

What is there to understand? The Tristate output never comes into play because pin 19 on both chips is hardwired to ground. That pin needs to see a high to put the outputs into the floating state, and it can never get there. The way things are set up on IC1, whatever goes in on an "B" input comes out on the corresponding "A" output.  IC2 is set up via jumper P1 to be just the opposite, Data in on A lines, out on B lines.

The thing in the lower right is a "title block".  It gives information on who made the drawing, when it was drawn, what it is used on, etc. That one is pretty basic.  On mechanical drawings, they also include stuff like scale, surface finish, material specs, etc.

[Zillolo]

What is there to understand? The Tristate output never comes into play because pin 19 on both chips is hardwired to ground. That pin needs to see a high to put the outputs into the floating state, and it can never get there.

The thing in the lower right is a "title block".  It gives information on who made the drawing, when it was drawn, what it is used on, etc. That one is pretty basic.  On mechanical drawings, they also include stuff like scale, surface finish, material specs, etc.

Sorry, my brain was malfunctioning again. I obviously meant the lower left corner.

Do you know of any reason anybody would hardwire pin 19 to ground?

[N2IXK]

Because their application doesn't need the tristate capability?

The stuff in the lower left shows the distribution of the 5V power supply rail. It has a power indicator LED, a reverse protection diode, and 3 bypass capacitors. 5V power goes to each of the '245 chips via pins 20 and 10.

[kc9qvl]

Building a cnc something? If you are going to build a design similiar to this Think I would just use one as output and one as input. and forget about theopto couplers, pwm, etc. Might be better to have more switches for things like end stops.