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CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Modifying Micromite software to use a 3.5in display Our readers often ask if it is possible to make software written for the Micromite BackPack V1 (February 2016; siliconchip.com.au/Article/9812) or V2 (May 2017; siliconchip.com.au/ Article/10652) which normally use a 2.8in touchscreen to instead work with the larger 3.5in display. At the very least, a different display driver is needed. The ILI9488 controller used on the 3.5in touchscreen does not have a native Micromite MMBasic driver, so we need to load an external CSUB library. This consumes around 6kB of library space, so it won’t fit if the original program comes close to filling the available flash memory space. Assuming the driver fits, rewriting the MMBasic code to function with the 3.5in display is possible, but it is tedious, time-consuming and requires thorough testing. That’s because these display controllers cannot perform scaling to fill the screen. Also, Micromite fonts are bitmap-based and cannot be resized easily, except in integer multiples. The 2.8in display has 320x240 pixels, while the 3.5in display has 480x320 pixels. Pixels would have to be mapped 2:3, which would appear chunky and grainy as this must be done on a per-pixel basis. Also, screen elements may be anchored to the different parts of the display, so they could become scattered confusingly around the screen. But there is another, easier solution. It tricks MMBasic into thinking that it is connected to a 320x240 display, so all display elements are where they should be. As far as the MMBasic program is concerned, it is connected to a 320x240 screen. The downside is that these 320x240 pixels are located in one corner of the larger screen, meaning that the entire 3.5in display area is not available. In fact, since the pixel pitch of the 3.5in display is smaller than the 2.8in display, the resulting active display area is actually smaller. Still, as long as you have 6kB of flash memory spare, it will give you a functional, working display. Most importantly, it will be the same as far as the software is concerned. All you need to do is load our Library file (available for download from siliconchip.com.au/Shop/6/5949) instead of the inbuilt LCD driver, usually done with the OPTION LCDPANEL command. The main part of the Library file is the ILI9488 driver that we have used previously. The MM.STARTUP subroutine runs when the Micromite starts up. This loads the driver, clears the display and then uses POKE commands to override the display driver resolution. After this, the display is indistinguishable (as far as MMBasic is concerned) from the ILI9341 display driver. By initialising and clearing the display before changing the resolution, the unused parts of the display are simply left blank. You could also add other commands here to set this area to a contrasting colour if needed. The POKE commands are as follows. You could modify the values to emulate other display sizes: ‘set width POKE WORD PEEK( WORD &H9D000094),320 ‘set height POKE WORD PEEK( WORD &H9D000098),240 The sequence of commands needed to configure the Micromite is as follows; these are also listed in the Library file. After loading Library.bas into the Micromite (eg, using MMEdit or TeraTerm), type: LIBRARY SAVE WATCHDOG 1 OPTION TOUCH 7, 15 GUI CALIBRATE GUI TEST LCDPANEL GUI TEST TOUCH While not elegant, this solution is fully functional and results in a pixelidentical image to what would be seen on a 2.8in screen. Here’s what a typical screen from the DDS Signal Generator (April 2017; siliconchip.com.au/ Article/10616) looks like. siliconchip.com.au Australia’s electronics magazine Following these steps, develop or load your MMBasic program. This solution will only work with the V1-V3 Micromite BackPacks (using the PIC32MX170 processor) and not the Micromite Plus. Tim Blythman, Silicon Chip. November 2021  53