PCF8574 (I2C Send bit)

[Help]

Hi,

You can connect, say, 4 (each has 8 latches) of them to 8-bit port and latch outputs using one control input: LE (latch enable) .. see drawing below ..

Please can you explain more detail! I feel i can understand something from you.

Thank You.

 

[IanP]

You can connect all D0s from 4(or more) 74373 in parallel to, say, P1.0 .. all D1s to P1.2 .. all D7s to P1.7 ..
Then you need to control the /LE pins; you can hook them up to 4 separate microcontorller pins, say, P2.0, P2.1, P2.3 and P2.4 ..

To output data on the 74373(1) set required data on PORT1 and make H-L-H transistion on P2.0 to latch the data in 74373(1) ..
If you make similar transiston on P2.1 you will latch data to 74373(2) .. and so on ..
Of course, the /OE pins of all 74373 have to be connected to 0V to enable outputs ..

Regards,
IanP

 

[Help]

Hi,

Thank! The below circuit is what you explain.

Thank You.

 

[IanP]

That's it ..

Just for your interst, some designers prefer 74LS573 as this IC has all inputs on one side and all outputs on the other ..

Regards,
IanP

 

[Help]

Hi,

If we want to do it as Input way. So we just in reverse connect. The 74573(1) Q1, 74573(2) Q1, 74573(3) Q1 connect in paraller.... 74573(1) Q2, 74573(2) Q2,..connect in paraller way and so on then the D1-D7 as our input. Am i right?

Thank You.

 

[IanP]

As inputs I wouldn't use 373 latches but 74LS245 (or similar) tri-state buffers ..
The concept is the same: all outputs connected together and only one 245 is active at a time ..

Regards,
IanP

 

[Help]

Hi,

Ya, you are right. we can not use 373 because so many input coming in at the same time and how can we LE the 373!! If using 245 we can do isolation between input and output. But can the 245 Latch the signal?

I think to extant the Output i think using 373, to extant the Input using 245! because the 245 don't have latch function as 373, am i right?

Thank You.

 

[manrayap]

Mr IanP.

I'm refer to ur diagram 8051-74373-8255.JPG. The 8255 RESET pin is connected to GND. My question is how the 8255 will reset during power on? Thanks