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Second-Generation Colour Maximite 2 This new CMM2 computer is compatible with the original described in mid-2020 and adds several great new features. These include more memory, higher-resolution video modes, 24-bit ‘true colour’, more controller inputs, better keyboard and mouse support and some new optional components like a super-accurate realtime clock. Part 2: assembly & use D itching the use of a microcontroller module like in the original CMM2 means there are more SMDs onboard, but overall it has simplified the design. Since many vendors are now supplying boards with the vast majority of the SMDs already soldered, the cost has been kept low and assembly is quick and easy. So we’ll get stuck into that before we describe some ways you can use it. Construction Fig.4 shows the PCB overlay for the CMM2 Gen2 board. You can use this as a guide during construction, but it is also helpful for debugging, testing or planning hardware expansion (eg, developing an add-on board for the computer). If you’re building your CMM2 Gen2 from scratch (including soldering all the SMDs), we’ll assume that you know what you are doing and just give some general pointers. Firstly, make sure that you have IC3 & IC4 orientated correctly before you solder more than a few pins. Even experienced constructors can sometimes mount ICs with pin 1 in the wrong location, and fixing it is a lot of work! siliconchip.com.au Words and MMBasic by Geoff Graham Design and firmware by Peter Mather After soldering IC3 and IC4, clean up the board and scrutinise the solder joints to ensure they’re all good and there are no bridges. You can mount the remaining SMDs in pretty much any order. Do check the orientation of the remaining ICs and oscillator modules before and after tacking them down. Once you have all the ICs, resistors, capacitors, oscillators and reset switch in place, give the board another clean, and you’re at the same point as someone who is starting assembly from one of the partially pre-assembled kits. Finishing your computer Even if you have a partially assembled second-generation Colour Maximite 2, you still need to complete it by soldering the connectors and larger components, a few of which are surface-mounted. This is reasonably straightforward; only a couple of items need to be treated with care. The first is the SD card socket, which should be soldered first so that you have easy access with the soldering iron. This is a surface-mounting connector, and it has two small pins on its underside which match two holes in the PCB. These help locate the Australia’s electronics magazine connector in the correct position while you solder the pins. The best approach in soldering this socket is to apply plenty of liquid flux on the pins and carry the solder to the joint on a fine-tipped, temperature-controlled soldering iron. You could also use fine-gauge rosin cored soldering wire and solder the joints directly, but this has the risk of adding too much solder causing shorts etc. Note that the socket must be held firm to the PCB while soldering, as any gap between it and the PCB will prevent an inserted SD card from making reliable contact with the connector pins. To start, solder the two tabs on the right-hand side of the socket (viewed from the front) and the five on the lefthand side. Some are close to the socket shield, so take care not to cause a solder bridge there. You can then solder the nine pins at the rear. If you get a solder bridge, don’t worry and carry on with the other pins. Finally, examine your soldering carefully and clean up any solder bridges using solder wick. Be careful here as solder wick can suck up all the solder (although generally, it will September 2021  61 Fig.4 (above): the overlay diagram for the Colour Maximite 2 Gen2. Shown below is the PCB with all the connectors, the SD card socket and the battery holder soldered in place. The large central IC is the ARM Cortex-M7 processor, which does most of the work. Above the processor is the 32MB RAM used for holding VGA images and providing extra memory for BASIC programs. leave enough behind). You should go back over the pins and resolder any that look like they don’t have enough solder. When you have finished, inspect each joint with a x10 or x20 magnifier. Also count the pins on the SD card socket; you should have soldered a total of 16 pins. We have found that most construction faults in this area have been missed pins and blobs of solder shorting to the shield of the SD card socket. The real-time clock cell holder is also surface mounted, but it is easy, and it also has two small pins on the underside which ensure the correct positioning. The locations of the remaining connectors are clearly marked by the silkscreen on the PCB, as well as being shown on Fig.4 and in the accompanying photograph, so they should drop in easily. Usually, the case is supplied by the vendor but, if not, you can purchase it as a standard item from Jaycar (Cat HB5970), Altronics (Cat H0472) or element14 (Cat 1526699). When mounting the PCB in the case, it needs 5mm spacers to be placed between the PCB and the four mounting posts. These raise the PCB and the connectors to match the cut-outs in the front and rear panels. Most vendors will also sell pre-cut and labelled front and rear panels to finish off the computer with a professional appearance. You can make the required cut-outs in the blank panels supplied with the case, but it is much easier to use the machine-cut panels. Getting started With the Colour Maximite 2 Gen2 built, you then need to load the firmware, which includes the MMBasic interpreter and the drivers for the hardware components (video, keyboard etc). You can download the firmware from the Silicon Chip website or the author’s website. There is only one version of this. It will automatically detect the hardware that it is running on (ie, the first- or second-generation designs) and configure itself accordingly. To load the firmware, you will need a desktop or laptop PC running Windows, Linux or macOS. There are two methods of loading the firmware using either a USB Type-A to Type-A cable or a Type-A to Type-B cable. Both methods do not require any additional 62 Silicon Chip Australia's Australia’s electronics magazine siliconchip.com.au hardware and are fully documented in the Colour Maximite 2 User’s Manual, which should be in the firmware download package. Here is a quick rundown of the steps involved in programming the STM32 chip. 01 Install the STM32 Cube programmer software from www. st.com/en/development-tools/ stm32cubeprog.html 02 Move the jumper on BOOT0 from RUN to PRG. 03 Plug the CMM2 Gen2 board into your PC using a USB cable. 04 Launch the STM32 Cube app. 05 Select USB at top right, refresh and connect. 06 Click the download button at left. 07 Browse to the firmware BIN file. 08 Tick Verify. 09 Start Programming. 10 Wait about five seconds for the write/verify process to complete. 11 Check that you get the ‘File Download Complete’ OK message. 12 Check that you get the ‘Verify OK’ message. 13 Unplug the CMM2 Gen2 from your computer 14 Move the BOOT0 jumper back to RUN. 15 Plug it back into your computer. With the firmware loaded, you should see the boot-up screen as shown in Screen 1. At this point, you can try typing in a command at the command prompt. For example, try this simple calculation: > PRINT 1/7 0.1428571429 See how much memory you have: > MEMORY Flash: 0K ( 0%) Program (0 lines) 516K (100%) Free RAM: 0K ( 0%) 0 Variables 0K ( 0%) General 24800K (100%) Free Count to 10: > FOR a = 1 to 10 : PRINT a; : NEXT a 1 2 3 4 5 6 7 8 9 10 Bubbles The next step is to try an actual program, such as the following. This will cover the screen in animated, overlapping coloured bubbles: siliconchip.com.au Oscillator Upgrade for the Colour Maximite 2 As described last month, the clock oscillator design in the first generation Colour Maximite 2 was adequate for the default 800x600 pixel VGA video resolution. However, with firmware upgrades, it is now possible to generate much higher resolutions. Still, they generally require the fitting of an external clock oscillator to eliminate jitter and instability in the video. If you have an original CMM2 and do not plan on using these high resolutions, you don’t need to perform this upgrade. Also, note that the second generation design described here already has this external oscillator fitted by default, so if you build the new version, nothing extra needs to be done. To perform the upgrade, you will need an 8MHz crystal oscillator in a 5x7mm SMD package (QX7 XO ≤ 25ppm) such as the Abracon ASV-8.000MHZ-EJ-T, and possibly a 100nF SMD ceramic capacitor in a 3.2x1.6mm (M3216 or imperial 1206) package. We sell these two parts through our website: siliconchip. com.au/Shop/7/5654 The PCB used in the first generation computer has provision for these parts. The solder pads are located under the Waveshare board near the left-hand 80-pin connector. Installing these parts can be tricky, so if you have not had any experience with soldering SMD parts, you should practice on something unimportant and take extra care. Also note that the solder pads are close to the 80-pin connector, so care also needs to be taken to avoid damaging this by accidentally touching it with the soldering iron. The oscillator has a dot identifying pin 1, and this needs to be aligned with the dot on the PCB silkscreen (it is tiny). With the oscillator correctly aligned, you can solder it with flux paste, a fine-tipped soldering iron and the minimum of solder. Be careful not to overheat the joint, and do not let the solder touch the case of the oscillator (which will short the connection to ground). The capacitor should be fitted after the oscillator. It is easier to solder and is not polarised. It is not necessary to remove the 8MHz crystal from the Waveshare board. The signal from the oscillator is strong enough to swamp the crystal, so it will have no effect. This strong signal might also damage the crystal, but this is not a problem as it is now surplus to requirements. DO CIRCLE RND*799, RND*599, RND*100, 1, 1, 0, RND*16777215 PAUSE 4 LOOP You can see the result of running this program in Screen 2. What the photo does not show is that the screen is quite lively, with bubbles of all sizes popping into existence, then being covered by subsequent bubbles. To enter this program, type the command below at the command prompt: EDIT “bubbles.bas” This will start the built-in editor where you can enter the above program. Once you have done this, press F2 (to save and run it), and you should see the screen fill with coloured bubbles. It will carry on forever; to interrupt it, press CTRL-C on your keyboard and you will be returned to the command prompt. Australia’s electronics magazine If you made an error when entering the program, MMBasic will stop the program and display an error message. You can then press the F4 key and that will take you back into the editor, with the cursor positioned on the line that caused the error. Correct the error and press F2 to save this new version and run it again. How does this program work? The DO and LOOP commands set up a loop that will continuously execute the commands inside the loop until interrupted. The CIRCLE command looks complicated, but it simply draws a circle at a random position with a random size and random colour. In MMBasic, the function RND generates a different random number from zero to 0.999999 every time it is used. We multiply this random number by 799 to give a number between zero and 799. This is the X-axis of the centre of the circle, and it will fit on the screen as the default video resolution is 800x600 pixels. Similarly, September 2021  63 Screen 1: when you have soldered the connectors in place, loaded the firmware and applied power, this is what you will be greeted with. You can see that we entered a few simple commands to prove that we have a working computer. multiplying RND by 599 will give us the Y-axis position. Next, multiplying RND by 100 gives a number between zero and 100, which is the radius in pixels. The following three parameters specify the line width (1 pixel), the aspect ratio (circular) and the colour of the circle’s border (black). The final parameter uses the RND function to generate a random colour from the 16 million-odd colours that the Colour Maximite 2 can display (16777215 is 224 − 1), and that colour is used to fill in the circle. The PAUSE 4 command on the next line pauses the program for 4ms after each circle is drawn. This slows down the creation of bubbles enough for you to admire the display. If you delete that line, you can appreciate the computer’s full speed – it is very fast, and the bubbles merge into a blur. Entering a program Screen 2: the result of running the “bubbles.bas” program described in the text. The screen is animated, with bubbles of all sizes popping into existence, then being covered by subsequent bubbles. Screen 3: the Welcome Tape is a collection of introductory programs accessible via an easy-to-use menu system designed for users new to the Colour Maximite 2. You can download it from https:// github.com/ thwill1000/ cmm2-welcome 64 Silicon Chip Australia’s electronics magazine This was briefly mentioned above in the “Getting started” section, but it deserves to be explained in more detail, as it is central to how the CMM2 is used. A program is a sequence of BASIC commands extending over many lines, so except for the most trivial programs, you won’t be typing commands in one at a time at the command prompt. You need a program editor, and the Colour Maximite 2 has such an editor built in. The editor includes colour-coded text (commands in cyan, comments in yellow etc), advanced search and replace, a clipboard for cutting and pasting and many more handy features. To invoke the editor, you must have an SD card inserted in the front panel slot, as the editor will save the edited file to this card. The command is: EDIT "filename" Where filename is the name of your program (it must be surrounded by double quotes). So, for example, type the following at the command prompt: EDIT "test.bas" This will start the editor, allowing you to edit the file “test.bas” on the SD card. If you have used a text editor before (or even a word processor), you will find that this one operates similarly. The arrow keys move the cursor around the text, the delete key deletes siliconchip.com.au the character under the cursor and the backspace key deletes the character before the cursor. At the bottom of the screen, the status line displays common functions such as F6 for save, ^F (hold CTRL and press the F key) for find and so on. At this point, you can try entering the standard program that most programmers typically use to test a new computer and programming language: “Hello World”. This might not sound like much, but in some cases, this involves installing software, getting to grips with complicated compiler requirements, reading lots of manuals etc. With the Colour Maximite 2, it is easy. Just start up the editor (as described above) and enter the line: PRINT "Hello World" Then press the F2 function key, and the editor will save and run your program with the result that the words “Hello World” should display on your screen. If you have made a mistake, an informative message will be displayed by MMBasic. You can then press the F4 function key, and you will be returned to the editor with the cursor placed on the line that caused the problem. The error can be corrected and by pressing F2 again, your modified program will be saved and run for another test. This ease-of-use is part of why the Maximite series of computers, first published by Silicon Chip ten years ago (starting in March 2011), has become so popular. Colour Maximite 2 Resources Since the introduction of the Colour Maximite 2, many people have had fun creating programs for this great little computer and others have gathered them into libraries that you can access. These are some of them: Colour Maximite 2 Welcome Tape: The Welcome Tape (Screen 3) is a downloadable collection of programs written by the user community that includes games, demonstrations and utilities. It is designed for firsttime users and is intended as an easy introduction to the Colour Maximite 2. See https://github.com/thwill1000/ cmm2-welcome The CMM2 Library: https://cmm2.fun is a wonderful collection of games, utilities and fun stuff written specifically for the Colour Maximite 2. It is presented as an easyto-browse list with screenshots, so you can easily select and download something that could cause you to waste a whole afternoon or evening of playing around. Even better, if you have written something useful, you can upload it to this library. The Fruit of the Shed: A huge catalog of information, code fragments, programming techniques for the Colour Maximite 2 and other devices that run MMBasic. For the Colour Maximite 2 content, go to http:// siliconchip.com.au/link/ab8u 101 BASIC Computer Games: If you were around in the late 1970s and playing with the computers of that era, you may know the book “101 BASIC Computer Games”, edited by David H. Ahl. This provides simple games that you could type in yourself and inspired a whole generation of budding programmers. Most will run on the Colour Maximite 2 with minor modifications. If you are into nostalgia, the book and its programs are available from this website: www.vintage-basic.net/ games.html The Back Shed: An online forum, where many users gather to discuss the Colour Maximite 2 and swap programs they have written. It is also a great place to get help, as many experienced people regularly contribute, including the designers of the Colour Maximite 2. You can find the forum at: www.thebackshed.com/ forum/Microcontrollers More information If you would like to know more about the Colour Maximite 2, browse the comprehensive User’s Manual, which is available in the download package from the Silicon Chip website and on the author’s website at http:// geoffg.net/maximite.html Also available from both sources is the free PDF “Introduction to Programming with the Colour Maximite 2”, which guides you through using the Colour Maximite 2, including a tutorial SC on programming in MMBasic. Enthusiastic users from around the world have written many programs, including games, for the Colour Maximite 2. Two of them include a modern representation of the Atari game Gauntlet and a version of the classic arcade game Pac-Man. siliconchip.com.au Australia’s electronics magazine September 2021  65