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Arduino UNO digital I/O


N5IB
 

I've been puzzling over how to configure the SSNA so at least it doesn't **prevent** the addition of a display. Better Arduino heads than mine may be needed for advice and counsel here.

I'm going under the presumption that the UNO has 14 digital I/O lines available. The DDS interface uses 4 (D8 - D11 at this time, but that can change).

Most LCD displays (parallel interface) need 8 data lines, an enable, a read/write line, and a clock. That adds up to 15. That may preclude the addition of a parallel display on the UNO. Of course a (more costly)  serial LCD would solve that problem. And the serial TX and RX lines are not used by the SSNA.

Jim, N5IB


glenn percy
 

 

--- In PHSNA@..., <phsna@...> wrote:


glenn percy
 

 


glenn percy
 

 


Nick Kennedy
 

Not sure what replies you have have already had since the Yahoo interface is acting a bit weird as to showing other messages in the thread.


I usually use the 4-bit version of the LCD interface.  Then an E and and RS line are needed.  You can tie the R/W line to "write only" usually.  So six lines are needed.


I've also been known to multiplex or share lines for multiple purposes.  If a line on the LCD is an input and the LCD will ignore it except when it gets a command to readthe data lines, you can use it for other purposes in the same project.


73, 


Nick, WA5BDU



N5IB
 

Thanks, Nick,

There certainly are 6 lines available. bits 0 and 1 are used up when the serial interface (even just the USB) is enabled. But the rest of the low 8 buts is uncommitted. So you send the data as a pair of nybbles?

Could you perhaps post a bit of info to help me and others. Suggest a display model that works in that mode (would need to be operable in a graphic mode) and if d2 - d7 would be appropriate to use.  If you have a circuit sketched that would be great. My only experience with LCDs has been ready-to-go kits, and programming the RS-232 interfaced ones.

Jerry did point out that the A/D lines can be used as digital. But the concern is introducing switching noise when reading adjacent pins as analog.

Jim, N5IB


Nick Kennedy
 

Oops, well I'm talking beyond my knowledge level here.  I was thinking of the standard LCD Hitachi interface.  I guess we'd be thinking TFT or something for the graphical screen.  Not sure what the standards are there for I/O.


I took a quick look at Adafruit and I see one that requires 14 (!) lines, but another that uses SPI says it just needs 4 or 5 digital pins to send data to the display.


Regarding multiplexing pins, I'm looking at my PIC log power board and I see that I have one pin that's used for data out to the LCD and for UART transmit, while another has three uses:  data to LCD, UART receive, and DDS clock.


73-


Nick, WA5BDU