0

Driving 2X RA8875 off of one microcontroller, can it be done
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Re: Driving 2X RA8875 off of one microcontroller, can it be

by adafruit2 on Sun Aug 09, 2015 7:53 pm

paulstoffregen wrote:
adafruit2 wrote:...and indicate to people to put in a 2K resistor in series to MISO, would that do it?


If you're willing to accept an undefined logic level at Arduino's MISO pin when accessing two or more of these displays, then why bother with the MISO wire at all? Summing the signals with resistors isn't going to give you a valid MISO signal when 2 are connected. You might as well just leave it unconnected.


oh right, i meant with a RA8875 on SPI and *some other* tristating device like SD card or whatnot. do people often request/try to use 2 displays? that seems like a really unusual case...???

adafruit2
Site Admin
 
Posts: 18666
Joined: Fri Mar 11, 2005 7:36 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by paulstoffregen on Sun Aug 09, 2015 8:45 pm

Well, this thread is about using 2X (or more) of these displays! :)

As far as I know, only 2 people have asked and 1 has actually tried to use multiple RA8875. I guess that counts as "a really unusual case".

I'm not counting myself, of course. I only looked into this because it was reported as 2 working (but 3 failing) on Arduino Mega, but only 1 worked on Teensy 3.1. Whenever a library is shown to behave differently between AVR-based Arduino and ARM-based Teensy, I usually dig into the details. In this case, the RA8875 MISO signals were conflicting on both boards, but 5V AVR has slightly different logic threshold.

Come to think of it... why would it fail at all if the MISO signal isn't ever used? Maybe there is some place it matters?

But yeah, this certainly is a very uncommon case on am already not very popular product, which already has a well documented (though inconvenient) solution.

paulstoffregen
 
Posts: 434
Joined: Sun Oct 11, 2009 11:23 am
Location: Portland, Oregon, USA

Re: Driving 2X RA8875 off of one microcontroller, can it be

by paulstoffregen on Sun Aug 09, 2015 8:52 pm

Really, if anything, as you design future SPI-based products, please please please remember to do the simple 2-resistor MISO check. It just takes a few minutes to connect 2 resistors and measure the DC voltage on MISO while the device is idle. If you don't get half the power supply voltage, please please please add the tri-state buffer before finalizing the breakout board or shield design!

And don't forget pullup resistors on all SPI chip select lines! Just yesterday I used an (admittedly older) Adafruit ILI9340 display for testing... which lacks those pullup resistors. Sometimes if works with the spitftbitmap example, other times it fails, depending on the random voltage on the SD card's chip select line while the Adafruit_ILI9340 library initializes the display chip! Just one little resistor would have made that product rock-solid with the library's examples.

http://www.dorkbotpdx.org/blog/paul/bet ... in_3_steps

paulstoffregen
 
Posts: 434
Joined: Sun Oct 11, 2009 11:23 am
Location: Portland, Oregon, USA

Re: Driving 2X RA8875 off of one microcontroller, can it be

by adafruit2 on Sun Aug 09, 2015 9:49 pm

yah going forward we can do that - alternately i can also just update the spibmp example to force the SD CS line high in setup()...or will that not work for some reason? there's also a bunch of libraries that need SPItransactioning. nowadays i do that for new SPI-using libs, but there's quite a few old ones.

readData is called to check status and also flip modes sometimes. this is unlike the ILI934x display which do not really have any status bits.

adafruit2
Site Admin
 
Posts: 18666
Joined: Fri Mar 11, 2005 7:36 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by eph_raim on Mon Aug 10, 2015 12:28 am

but still with the MISO problem can i still continue to my project using two ra8875 and one arduino .. i just need a stable answer in which i can base my school project. hope you can help me with this.. iwould just need to know how to deal with it on making a keyboard as an input and the two lcds thats connected to two ra8875 and an arduino as an output .. thankyou

eph_raim
 
Posts: 14
Joined: Sat Aug 08, 2015 9:21 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by paulstoffregen on Mon Aug 10, 2015 1:01 am

eph_raim wrote:but still with the MISO problem can i still continue to my project using two ra8875 and one arduino .. i just need a stable answer


Yes, you can. You *MUST* connect the 2 displays has we have told you, using the 74HC125 chip. Follow the diagram and photo, and it will work.

Two people, Dani and I, have confirmed it does work. We both connected the displays and made them work and we posted photos. Is that a stable enough answer for you?

paulstoffregen
 
Posts: 434
Joined: Sun Oct 11, 2009 11:23 am
Location: Portland, Oregon, USA

Re: Driving 2X RA8875 off of one microcontroller, can it be

by eph_raim on Mon Aug 10, 2015 4:31 am

Thankyou sir paul!

eph_raim
 
Posts: 14
Joined: Sat Aug 08, 2015 9:21 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by eph_raim on Fri Oct 02, 2015 8:32 am

I have a question is ther a difference between the codes for the tft lcd and no tft lcd?.. is there a code on how can i use a keyboard as an input device to display txt on the lcd.? and lastly how can i insert emoticons on the codes.. thankyou for answering ;)

eph_raim
 
Posts: 14
Joined: Sat Aug 08, 2015 9:21 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by eph_raim on Sun Oct 04, 2015 12:37 am

Another question is what happen to my circuit.. i follow all the instructions but i dont know what happen.. when wires were connected to the rst line the display doesnt show anything but when i accidentally connect the wire to the wait pin the display works like the images showed by local dani and paul.. displaying hello world .. what just happen there can someone please help me and give a solution for these thankyou ... badly needed your help adafruit ,local_dani, and sir paul

eph_raim
 
Posts: 14
Joined: Sat Aug 08, 2015 9:21 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by adafruit_support_rick on Sun Oct 04, 2015 11:24 am

Please post some pictures of your setup and wiring

adafruit_support_rick
 
Posts: 35095
Joined: Tue Mar 15, 2011 11:42 am
Location: Buffalo, NY

Re: Driving 2X RA8875 off of one microcontroller, can it be

by riadanza on Mon Oct 05, 2015 8:39 am

If I'm only using one display I'm assuming I still need to use 74HC125 for my other devices that use SPI (like the SD card, etc.)?

Thank you,
Robert

riadanza
 
Posts: 21
Joined: Tue May 12, 2015 9:14 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by paulstoffregen on Mon Oct 05, 2015 8:55 am

Yes, if you connect any other chip which uses MISO, you *MUST* use a '125 or similar tri-state buffer on the RS8875's MISO signal, to prevent the RA8875 from driving MISO while the other chip is in use.

This should be clear from all the discussion, but just in case it is not clear, you *MUST* use a tri-state buffer if any other SPI chip with a MISO signal is used. It is absolutely required. Please consider this a final answer. There is no question, no doubt, the tri-state buffer chip is needed.

paulstoffregen
 
Posts: 434
Joined: Sun Oct 11, 2009 11:23 am
Location: Portland, Oregon, USA

Re: Driving 2X RA8875 off of one microcontroller, can it be

by riadanza on Mon Oct 05, 2015 9:36 am

Thank you, that's clear. Much appreciated.

riadanza
 
Posts: 21
Joined: Tue May 12, 2015 9:14 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by eph_raim on Tue Oct 06, 2015 9:53 am

Sir i have a question.. how can i connect the ra8875 to display the text that i inputted from the keyboard. The setup i follow is the one sir paul gave.. the only problem is i cant display the txt to the ra 8875 driverboard with lcd screen

eph_raim
 
Posts: 14
Joined: Sat Aug 08, 2015 9:21 pm

Re: Driving 2X RA8875 off of one microcontroller, can it be

by adafruit_support_rick on Tue Oct 06, 2015 10:42 am

Well, have you written a sketch to allow you to do that? Can you post your sketch?

adafruit_support_rick
 
Posts: 35095
Joined: Tue Mar 15, 2011 11:42 am
Location: Buffalo, NY

Please be positive and constructive with your questions and comments.