LCD interfacing using Data Bus

[StupidDum]

I am working on a microprocessor, want to reduce the GPIO used for futhre expansion. Therefore, I wish to connect the LCD to data bus to save pins.

Is that possible to connect the LCD data bit directly to microprocessor data bus, then E, CS, RW to GPIO??? Or should it require some latch or buffer?

 

[Nigel Goodwin]

What processor are you talking about?.

 

[kinjalgp]

Check this schematic:
https://www.pjrc.com/tech/8051/board5/schematic.html

It shows how to interface a LCD to 8051's data bus.

 

[StupidDum]

nowadays microcontroller is so powerful, that many things can be done using microcontroller. that result in less attention to microprocessor.
now i starting to explore on microprocessor that use address, data bus.

i read that there must be tri-state buffer or output for components which are connected to the bus. therefore i want to know if i could connect lcd directly to the data bus. seem like this is neceesary.

thanks for your schematic, kinjalgp.

 

[JohnBrown]

It all depends on the micro you are using. You'll need address decoding, otherwise the LCD will occupy the entire address space, and you'll need to check the timing of such things as E, CS R/W. There is no simple answer. It's down to the particular LCD and micro.

 

[checkmate]

nowadays microcontroller is so powerful, that many things can be done using microcontroller. that result in less attention to microprocessor.
now i starting to explore on microprocessor that use address, data bus.

i read that there must be tri-state buffer or output for components which are connected to the bus. therefore i want to know if i could connect lcd directly to the data bus. seem like this is neceesary.

thanks for your schematic, kinjalgp.

Just for interest sake, what microprocessor are you using that provides GPIO pins? Because by definition, uPs don't have them.

Anyway, to answer your questions, for a chip interfaced to a data bus, all output pins has to be made open-collector. An open collector output can only sink but not source current. Think of it having the capability of pulling the line to ground, but otherwise floats the line. You can probably figure out the reason when you have multiple chips sharing the same bus.

Most chips meant for bus interfacing already have this capability. If the chip you want to use doesnt, then there are several alternatives. Using tri-state buffers is one of them, though it's probably cheaper to use open-collector buffers.

 

[Nigel Goodwin]

Just for interest sake, what microprocessor are you using that provides GPIO pins? Because by definition, uPs don't have them.

I asked him that right at the beginning of this thread, but he never replied!. GPIO is a term usually associated with the small 8 pin PIC's, as you only have one port they don't bother calling it PortA, just GPIO.

Anyway, to answer your questions, for a chip interfaced to a data bus, all output pins has to be made open-collector. An open collector output can only sink but not source current. Think of it having the capability of pulling the line to ground, but otherwise floats the line. You can probably figure out the reason when you have multiple chips sharing the same bus.

Most chips meant for bus interfacing already have this capability. If the chip you want to use doesnt, then there are several alternatives. Using tri-state buffers is one of them, though it's probably cheaper to use open-collector buffers.

I think tristate buffers and address decoders would be the way to go, with open copllector you need to ensure that the transistors are switched off - and you might not be able to guarantee it. Really it's 30 year old technology!.

 

[StupidDum]

...GPIO is a term usually associated with the small 8 pin PIC's, as you only have one port they don't bother calling it PortA, just GPIO...

It is not always gotta be PIC.
well, i'm using Zilog. GPIO is just a name to general purpose IO pins, instead of calling it as " pins on Port A, B, C, D...."
On Zilog, there are dedicated pins, and also GPIO that are multiplexed.

 

[checkmate]

So what's your processor you are working on?

 

[StupidDum]

Zilog eZ80L92