Can I treat a max7221 as DOUT with 2 SRs?

MIOS programming (C)
1

I was looking at ways to hook up a max7221 to the midibox. I am always thinking in terms of retaining the functionality of a midbox64 but being able to change how certain things are done.

I know there was a max72xx driver created as part of the Stribe project in the repository However I am not sure how to hook this up to core if I am using it for DOUT, DIN and AIN modules as well.

I am also trying to avoid re-inventing the wheel or writing too much new code since the BLM project already exists and works well.

I was wondering if I could just connect a max7221 chip in place of where two 74HC595’s on a DOUT module would be and then used the normal MIOS code for writing to a dout module to control it? (as long as I read the max7221 data sheet and sent the appropriate values to control it… e.g. I may have to write a few of my own functions for it)

I could also do all this stuff with just the standard DOUTs but then I lose the ability to easily control the broghtness of each led matrix I drive. I want to use three cascaded max7221 chips to drive an rgb led matrix of 8x8. It is nice that each one only needs a single resistor value to set the brightness of the whole colour.

I could also do this with the 74HC595 by pwm the chip enable pin  BUT how do I program this into mios? what pin do I use as the pwm output? Should I get a dedicated square wave generator to do this? If so, how do I control it with software?

2

Controlling a MAX7221 via DOUT interface requires a lot of programming skills, because you need to know, how to write a “sequential state machine” which controls the register write accesses on each SRIO update cycle.

PWM: see this article

However, I think, that the application has enough spare pins to drive the chip via GPIOs (only the CS# line should be a dedicated output, all others can be shared).

The README describes, how to adapt the pins - it’s easy!

Best Regards, Thorsten.

3

heheh EASY for you! :wink:

Those pins (from port C) are being used by the AIN module no? (J6 on the core).  What other pins could I use as GPIO?

With something like Arduino it is so clear what one has assigned to each pin and how those pins will be used. I guess with MIOS I am still getting lost between what has already been pre-allocated in MIOS and what I can override or assign with my C apps. Still hazy on elements of the big picture…

Also I don’t know what LATC and TRISC are.

I assume “shared with other outputs” means that two of those pins can use a port/pins that will also be used for other purposes (they take turns) but the CS pin needs to be dedicated.

I may be missing something really obvious or simple about how to integrate this into MB64 or simmilar app that has AIN, DIN and DOUT modules attached to it.

thanks!

4

With something like Arduino it is so clear what one has assigned to each pin and how those pins will be used. I guess with MIOS I am still getting lost between what has already been pre-allocated in MIOS and what I can override or assign with my C apps. Still hazy on elements of the big picture…

I guess, that you missed the pin list: http://www.ucapps.de/mios/mios_pin_list.txt

I would propose to start with pin RC4, RC5, RD4 (I guess, that you are not using touch sensors)

In order to assign these pins, add following lines to the Makefile:

[tt]

include MAX72xx driver

MAX72XX_DEFINES += -DMAX72XX_CHAINLENGTH=1

MAX72XX_DEFINES += -DMAX72XX_LAT_CS=LATC -DMAX72XX_TRIS_CS=TRISC -DMAX72XX_PIN_CS=4

MAX72XX_DEFINES += -DMAX72XX_LAT_SCLK=LATC -DMAX72XX_TRIS_SCLK=TRISC -DMAX72XX_PIN_SCLK=5

MAX72XX_DEFINES += -DMAX72XX_LAT_DIN=LATD -DMAX72XX_TRIS_DIN=TRISD -DMAX72XX_PIN_DIN=4

include $(MIOS_PATH)/modules/max72xx/max72xx.mk

[/tt]

LATx and TRISx are described in the PIC datasheet. For you it’s probably sufficient to know, that they control the pin output value and tristate driver

Btw.: this is how you can add the driver into a C application. I assume that you will do the first experiments in C to save time. I’m currently a bit too lazy to describe the differences between defining constants in assembly (which would be done in main.inc) and in C (where it is done in the makefile)

However, the AOUT driver is a nice example which shows the differences (e.g., have a look into the most recent MBSID/MBFM/MBSEQ or MBCV code)

All the documentation issues are btw. a big blocking point for me, which prevents me from releasing the programming platform. I fear, all the different possibilities makes it too complicated. :frowning:

Best Regards, Thorsten.

5

There’s also an expanded pin list on the wiki… It’s pretty much the same, but has some added info.

http://www.midibox.org/dokuwiki/mios_pin_list

If you need help adding modules, just shout out.

6

I had seen those documents before but I simply forgot them :stuck_out_tongue:

Thanks a lot for the help guys!