Colour Maximite 2
(Generation 2)
Part
2
Words
Phil Boyce
Design
Geoff Graham
Firmware
Peter Mather
Assembly and setup of our retro home computer
L
ast month, we introduced
the new, and extremely powerful,
Colour Maximite 2 Generation 2
computer (CMM2 G2, or just ‘G2’ for short).
The specification and features list (see
Part 1, last month) shows that this latest
version of the Maximite certainly packs a
lot of punch into a small package. Fig.1
shows various screenshots from different
programs, and from these you can begin to
get an idea of the G2’s graphics capability;
and do remember that all these programs
are coded in BASIC.
In keeping with all previous versions of
the Maximite family, the G2 makes for a
very rewarding self-assembly electronics
project. Fig.2 shows that the G2 PCB
contains many surface-mount devices
(SMDs); however, don’t let this put you
off building it yourself. I guarantee that
even if you have never soldered an SMD
component before, providing you can
use a soldering iron with through-hole
components then you will be more than
able to build the kit version of the G2; and
probably complete it in just a couple of
hours. If you look at the circuit diagram
in Fig.3, you may be wondering why I am
so confident with this claim. Put simply,
the G2 kit contains a part-assembled PCB
that just needs finishing off with a handful of through-hole parts.
Fig.1. Various screenshots from some early programs showing
the potential of the G2’s impressive graphical output – all coded
in MMBASIC.
42
PCB, kit, or fully assembled?
The G2 PCB has been optimised for automated machine assembly, but what does
this actually mean? Well, you could use
the PCB Gerber files (supplied in this
month’s downloads from the November
2021 page of the PE website) and get a
PCB made from one of the many Far-East
PCB fabricators. You would then need to
painstakingly solder all the SMDs yourself. I have done this on several occasions
when the prototype was being developed;
however, this method of assembly does
require you to be extremely confident
with SMD soldering, not to mention very
patient – especially when soldering the
Fig.2. The assembled (4-layer) G2 PCB mostly contains SMDs,
all mounted on the top side. Around the edge, there are a
handful of connectors, sockets and through-hole components.
Practical Electronics | November | 2021
176-pin STM processor. For most people, this assembly approach
is not an option (and is not one that I would recommend). Instead,
you can request that the PCB fabricator use their automation tools
for soldering the SMDs for you. To do this, you need to supply
two additional files alongside the Gerber files – the BoM and CPL
(Bill of Materials and Component Layout).
The list of SMDs that the PCB fabricator can solder for you are
shown in Parts List 1, and this should result in you receiving a
board with most of the SMDs pre-soldered (see Fig.4). This saves
a lot of soldering time, and also eliminates any silly mistakes
and/or damage to SMDs. It is then just a matter of soldering the
remaining components by hand, and then carefully fixing the
assembled PCB (Fig.2) into the recommended enclosure. This
approach is a much more practical assembly method and what
we recommend if you wish to build your own G2. To save you
having to deal with the PCB fabricator, and generating the two
assembly files in the correct format (often specific to whichever
fabricator you use), all the parts required to perform this process
are included in the kit version of the G2. However, if this still
seems like too much soldering, then you’ll be glad to hear that
the G2 is also available as a ready-assembled unit.
NOTE: As discussed last month, sourcing the required STM32
processor is currently very dificult. This is frustrating, but outside
of our control, so it may be a while before the STM32 becomes
readily available again from the manufacturer.
Assembling the kit
See Parts List 2 for what is included in the G2 Kit. It includes the
part-assembled PCB, along with all the connectors, sockets and
through-hole components required to finish the PCB (in other
words – the parts that the PCB fabricator won’t assemble). Also
included is the case, front and rear panels and all the mounting
hardware to fix the PCB into the case. We will now briefly step
through these items in the correct sequence to end up with a
complete working G2 kit.
Begin with the IR receiver, ensuring that the rounded face is
closest to the edge of the PCB (this is the receiver side which detects any incoming IR signal, so it needs to be outward facing).
Ensure you push it down all the way into the PCB (rather than
‘floating’ in the air). This will ensure it lines up with the ‘IR window’ hole in the front panel.
Next, mount the dual LED assembly, mounting it flush with
the PCB. Next is the SD socket, and even though this is an SMD
component, the spacing of the pins is large enough to make soldering it in place very straightforward. Do not worry if you don’t
have a temperature-controlled soldering iron (a bit of a misconception is that you must have one if you’re soldering SMDs). I
recommend a standard iron which has a power rating of 15-25W.
The important point to bear in mind is not to leave the iron on
any one of the SD socket’s pins for too long as this could melt
the plastic body that holds the pins in place. Liquid flux and a
clean soldering iron tip is the key to a neat finish. The SD socket
has a pair of plastic locating pins on the underside that holds it
in correct alignment while soldering it in place. Begin by soldering the four larger corner pins (legs), then move onto the nine
pins on the back edge, followed by the three pins on one side.
Next, solder in the stereo socket. This is also an SMD component with locating pins to assist with alignment. Once positioned,
solder the five pins, but do be careful not to allow too much solder
to form on any one pin. Use de-soldering wick if you do end up
with excess solder on any joint. Next, solder the power switch
into position – nothing to point out here apart from ensuring it
remains upright (and at right-angles) to the PCB.
The coin-cell holder is another SMD component, but with
only two large legs to solder. Ensure that the holder’s orientation matches the shaped outline shown on the silkscreen
(otherwise the battery will connect into the circuit with reverse polarity!). Do not install the battery at this stage – that
comes at the end of assembly.
Practical Electronics | November | 2021
Next, mount the four connectors across the back-edge of
the PCB. These are all through-hole parts so nothing to really mention other than to ensure that they all sit flush on the
PCB. Once they’ve been soldered in place your PCB should
look similar to Fig.2 (but with nothing in IC5’s location near
the top-left corner).
Finally, solder the two 3-way headers into place. The BOOT
header (JP2) is the one that is close to the top-left corner of the
SD socket; and the PWR header (JP1) is the other one between
the stereo socket and the power switch. Slide the two jumper
links into place – one into the ‘PRG’ position (ie, the left two
pins of the BOOT header), and the other jumper link onto the
top two pins of the PWR header (closest to C11). The latter
makes the power switch active in the down position.
That completes the electrical assembly of the G2, so before
we proceed it is now worth doing a thorough visual check of
all the joints on the parts just soldered to ensure there are no
shorts. Once you’re happy with your soldering, place the PCB
onto a cleared working surface so that there is no risk of any
damage. I like to use the bottom half (the base) of the enclosure
as this minimises the risk of accidentally placing the PCB onto
any odd strand of metal which could damage it.
Initial testing
Before we load the MMBASIC firmware into the STM32 processor, it’s worth testing how much current the unit draws
from a 5V PSU. For this test, you will need a meter capable of
measuring up to a minimum of 250mA and a 5V supply that
supplies at least 300mA. I like to use Raspberry Pi PSU along
with a decent thickness USB type-B lead. At around £8, these
PSUs are relatively cheap, yet are more than capable of supplying enough current.
To measure the current, attach only the 5V PSU, and if you’re
not using a lab power supply, then you can put your meter
leads across the 3-way PWR jumper (JP1). Place one probe on
the bottom pin of the 3-way PWR header, and the other probe
on either of the top two pins (or onto the jumper link if it has
exposed metal). With the power switch in the up position
(off), your meter will short out the 5V rail from the USB socket
(CON2) direct to the 3.3V voltage regulator (REG1) allowing
you to measure the current draw.
If everything is OK, you should see a reading of around
50mA. If you observe something significantly different to this,
then first check that the PSU is indeed outputting 5V, and if
so, thoroughly re-check all solder joints resolving any issues
you find. Excessive current draw indicates that there is likely
to be a solder short somewhere (or a misplaced component).
Fig.4. A PCB fabricator can pre-solder all the smaller SMD
components, resulting in a board like this.
43
1 0 0 nF
1 6
4
1 5
U SB T Y P E B
P W R / C O N SO L E
1
4
2
D –
2 x
1 0 k Ω
+ 3. 3V
V cc
V 3
1 2
D C D
6
5
3 D +
C O N 2
IC 8
C H 34 0 G
U D –
U D +
8
1 0
D SR
X I
T X D
X O
C T S
G N D
3
2
+ 3. 3V
9
1
1 0 0 nF
+ 3. 3V
9
4 3 4 9
1
1 4
V D D
V D D Q
4 0
1 9
N C
W E
C AS
R AS
C S
38
C K E
37
C L K
IC 4
MT 4 8L C 1 6 M1 6 A2
39
D Q MH
1 5
D Q ML
2 1
2 0
BA1
BA0
2 3
A0
2 4
A1
2 5
A2
2 6
A3
6
V SSQ
1 2 4 6
52
V SS
2 8 4 1
T O
T O
AU D I O
C O N 4
X 3 1
4
ST
V D D
MO D E
8MH z
X O O U T 3
J P 7
G N D
3
6 x
1 0 0 nF
1 6
1 7
1 8
1 0 0 nF
1 µ F
1 0 µ F
1 1
R I
R X D
7
1 2 pF
1 0 Ω
1 3
D T R
R 2 32
1 2 pF
1 4
R T S
X 1 32 7 6 8H z
2 7
2
T O
N U N C H U K 1
53
D Q 1 5
51
D Q 1 4
50
D Q 1 3
4 8
D Q 1 2
4 7
D Q 1 1
4 5
D Q 1 0
4 4
D Q 9
4 2
D Q 8
1 3
D Q 7
1 1
D Q 6
1 0
D Q 5
8
D Q 4
7
D Q 3
5
D Q 2
4
D Q 1
2
D Q 0
36
A1 2
35
A1 1
2 2
A1 0
34
A9
33
A8
32
A7
31
A6
30
A5
2 9
A4
54
A3 O N C O N 1
A2 O N C O N 1
4 .7 k Ω
4 .7 k Ω
2 .2 µ F
2 .2 µ F
1 57
P G 1 4
1 56
P G 1 3
1 1 1
P G 7
1 2 0
P A9
1 2 1
P A1 0
1 6 4
P B6
1 52
P G 9
2 6
P F 8
2 7
P F 9
2 9
P H 0 / O SC _ I N
30
P H 1 / O SC _ O U T
1 51
P D 7
4 5
P A2
80
P B1 1
9 8
P D 1 0
9 7
P D 9
9 6
P D 8
7 8
P E 1 5
7 7
P E 1 4
7 6
P E 1 3
7 5
P E 1 2
7 4
P E 1 1
7 3
P E 1 0
7 0
P E 9
6 9
P E 8
6 8
P E 7
1 4 3
P D 1
1 4 2
P D 0
1 0 5
P D 1 5
1 0 4
P D 1 4
1 0 6
P G 2
6 7
P G 1
6 6
P G 0
6 5
P F 1 5
6 4
P F 1 4
6 3
P F 1 3
6 0
P F 1 2
2 1
P F 5
2 0
P F 4
1 9
P F 3
1 8
P F 2
1 7
P F 1
1 6
P F 0
1 0 8
P G 4
1 0 9
P G 5
1 6 9
P E 0
1 7 0
P E 1
1 1 2
P G 8
84
P H 7
58
P B2
1 0 1
P D 1 3
1 0 0
P D 1 2
9 9
P D 1 1
83
P H 6
59
P F 1 1
1 6 0
P G 1 5
4 6
P H 5
1 2 3
P A1 2
1 2 2
P A1 1
50
P A4
51
P A5
1 2 5
V C AP
81
V C AP
V SSA
1 7 2
1 59
1 4 9
1 36
1 0 3
1 2 7
82
+ 3. 3V
IC 3
ST M32 H 7 4 3I I G
4
6 C O M2 : T x
8
5
6
C O N 8
P A1 4
P A1 3
G N D
1 3
1
P E 2
9 2
P B1 2
1 4 5
P D 3
1 4 4
P D 2
1 4 1
P C 1 2
1 39
P C 1 0
1 4 0
P C 1 1
89
P H 1 2
1 1 0
P G 6
57
P B1
32
P C 0
87
P H 1 0
86
P H 9
85
P H 8
4 4
P H 3
4 3
P H 2
1 7 6
P I7
1 7 5
P I6
1 7 4
P I5
1 7 3
P I4
1 54
P G 1 1
1 50
P D 6
1 55
P G 1 2
3
P E 4
1 1 V E R T SY N C
P I9
1 2 H O R I Z SY N C
P I1 0
P I1 1
2
SD A
1
3
5
7
R ST
SD A
SC L
7
C O M2 : R x
1 33
P I2
1 32
P I1
1 31
P I0
1 30
P H 1 5
1 53
P G 1 0
1 2 8
P H 1 3
5
P E 6
4
P E 5
2
1 6 5 I C # 2 SD A
P B7
2
1 6 8 I C # 1 SD A
P B9
2
1 6 7 I C # 1 SC L
P B8
33 C O U N T 1
P C 1
1 2 9 C O M2 : R x
P H 1 4
C O U N T 2
34
P C 2 _ C
35 C O U N T 3
P C 3_ C
1 6 3 SP I 1 MO SI
P B5
1 6 2 SP I 1 MI SO
P B4
1 6 1 SP I 1 C L K
P B3
P W M1 C
56
P B0
1 1 6 P W M2 B
P C 7
1 34 G P I O
P I3
9 4 SP I 2 MI SO
P B1 4
4 1 C O M1 : D E
P A1
9 3 SP I 2 C L K
P B1 3
9 5 SP I 2 MO SI
P B1 5
1 1 5 P W M2 A
P C 6
G P IO
7
P I8
2
88 I C # 2 SC L
P H 1 1
55 G P I O
P C 5
C O U N T 4
54
P C 4
53 P W M1 B
P A7
1 38 F AST C O U N T
P A1 5
C O M2 : T x
4 0
P A0
P W M1 A
52
P A6
C O M1 : R x
4 7
P A3
C O M1 : T x
4 2
P A2
1 1 9
P A8
2
P E 3
V SS
T O
T O
B3 O N
B2 O N
1 58
5
R E SE T
8
1 4 8
P A1 3
SC L
1 0 0 nF
1 35
4
SQ W / I N T
V BAT
1 2 6
3
G N D
4
C R 1 2 2 0
BAT T E R Y
6
1 1 3
P A1 4
V BAT
IC 7
D S32 31 MZ
1 0 2
3
2
z
7 1
1
32 kH
6 1
V cc
1
R ST
1 6 6
BO O T 0
1 0 7
P G 3
80
P B1 1
31
R ST
1 7 1
P D R _ O N
V BAT
8
P C 1 3
2 4
P F 6
2 5
P F 7
2 8
P F 1 0
1 4 7
P D 5
1 4 6
P D 4
1 37
P A1 4
1 2 4
P A1 3
9
P C 1 4 / O SC 32 _ I N
4 5
P H 4
1 0
P C 1 5/ O SC 32 _ O U T
7 9
P B1 0
1 1 8
P C 9
1 1 7
P C 8
39
V D D A
38
V R E F +
4 8
2
1 0 0 nF
ST - L I N K
3. 3V
V D D
6
9 0
+ 3. 3V
P O W E R
9 1
4 .7 µ F
1 4 x
1 0 0 nF
6 2
1 µ F
7 2
1 0 0 µ F
G N D
4 9
1 0 µ F
S1
2 2
P W R
+ 3. 3V
+ 3. 3V
2 3
O U T
IN
36
R E G 1 AMS1 1 1 7 - 3. 3
1 4
+ 5V
1 5
J P 1
37
T O C O N 3
P I N S 37 & 39
J P 3
J P 4
C O N 1
C O N 1
Fig.3. The circuit diagram highlights that the G2 is built around the STM32
processor. There are just a handful of connectors, sockets and support
components directly connected to the STM32. Three other support ICs (RAM,
USB driver, and real-time clock), and one optional IC (for using a USB-protocol
COLOUR
MAXIMITE
2 GEN2
MAIN
CIRCUIT
mouse) complete
the circuit.
(Diagram courtesy
of Silicon
Chip
magazine)
USB driver
44
Practical Electronics | November | 2021
To install the MMBASIC firmware into
the STM32 processor, you simply need
to connect the G2 to a computer (this
can be either a Windows PC or Mac)
BO O T 0
+ 3. 3V
+ 3. 3V
2 .2 Ω
E SP _ 3. 3V
1 0 0 nF
1 0 k Ω
1 0 k Ω
1 0 0 µ F
1 k Ω
R E SE T
J P 2
1 k Ω
4 .7 k Ω
3
2
A
S2
1 0 0 nF
R ST
1 0 k Ω
A
λ P
O W E R
SD
λ
C AR D
K
K
1
IC 2
V cc
D Q
1 0 0 nF
DS18B20
DIGITAL
THERMOMETER
T SO P 4 838
I R SE N SO R
3
1
λ
G N D
P R O G /R U N
IR D 1
2
2 .2 Ω
L E D 1
1 0 µ F
1 0 0 nF
C AR D
P R E SE N T
SD
C O N 6
C AR D SK T
C D
2 4 0 Ω
2 4 0 Ω
V E R T SY N C
2 4 0 Ω
H O R I Z SY N C
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
9
C AR D E N ABL E
D AT A T O C AR D
2 4 0 Ω
1
2
3
2 4 0 Ω
C L O C K T O
4
C AR D
5
6
7
8
D AT A F R O M C AR D
1 2 0 Ω
1 2 0 Ω
1 2 0 Ω
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
1 2 0 Ω
1 2 0 Ω
2 4 0 Ω
1 2 0 Ω
2 4 0 Ω
1 2 0 Ω
1 2 0 Ω
C AR D
W R IT E P R O T E C T
C O N 5
V G AC O N N E C T O R
7 5Ω
2 4 0 Ω
1 2 0 Ω
V ID E O
V ID E O
1 2 0 Ω
1 2 0 Ω
1 2 0 Ω
1 2 0 Ω
7 5Ω
1 2 0 Ω
1 2 0 Ω
W P
– R E D
– G R E E N
2
– BL U E
3
V ID E O
7 5Ω
C O N 9
6
1 1
7
1 2
8
1 3
9
1 4
1 0
1 5
1
4
5
( H E AD E R F O R C O N N E C T I N G
E SP - 0 1 W I F I MO D U L E )
2 4 0 Ω
2 4 0 Ω
1 2 0 Ω
2 4 0 Ω
2
I C
2 4 0 Ω
1 2 0 Ω
2 4 0 Ω
IC 3P I9
2 4 0 Ω
IC 3P I1 0
1 2 0 Ω
1 2 0 Ω
1 2 0 Ω
1 2 0 Ω
2
I C
# 2 SD A
2 4 0 Ω
2 4 0 Ω
2 4 0 Ω
2
I C
2
I C
1 2 0 Ω
V E R T SY N C
H O R I Z SY N C
T O
N U N C H U K 2
1 0 k Ω
# 2 SD A
# 1 SD A
# 1 SC L
+ 3. 3V
1 0 k Ω
C O U N T 1
C O M2 : R x
C O U N T 2
C O U N T 3
SP I 1 MO SI
SP I 1 MI SO
SP I 1 C L K
1 0 k Ω
P W M1 C
P W M2 B
G P IO
SP I 2 MI SO
+ 3. 3V
C O M1 : D E
C O M2 : T x
P W M1 A
C O M1 : R x
C O M1 : T x
2
I C
# 2 SD A
2
# 2 SC L
I C
I C 5_ P I N 1 8
I C 5_ P I N 1 7
via a single USB (type-B) lead (this single lead will also supply power to the
G2 from your computer’s USB port).
However, you might need to install a
USB driver first so that your computer’s
Practical Electronics | November | 2021
7
G P IO
C O U N T 4
P W M1 B
F AST C O U N T
2 8
30
32
34
36
38
4 0
C O N 3
E X T E R N AL
I/O
9
1 1
1 3
1 5
1 7
1 9
2 1
2 3
2 5
2 7
2 9
31
33
35
37
39
# 2 SC L
1
3
5
2
I C
4
6
8
1 0
1 2
1 4
1 6
1 8
2 0
2 2
2 4
2 6
P W M2 A
G P IO
2
SP I 2 C L K
SP I 2 MO SI
+ 5V
1 0 k Ω
C O U N T 4
P W M1 B
F AST C O U N T
C O M2 : T x
P W M1 A
C O M1 : R x
C O M1 : T x
operating system (OS) can detect the
G2. The G2 uses the popular CH340G
USB-to-serial IC (IC8) and the relevant
driver can be downloaded and installed
from here: https://bit.ly/pe-nov21-drv
Once installed, connect the G2 to your
computer and check it can detect the
G2 (for example, use Windows Device
Manager and see which COM port has
been assigned to the G2).
45
8mm M3 bolt
Motherboard
5mm M3 spacer
ABS case with mounting pillar
Fig.5. The PCB is fitted to the base using
four 5mm nylon spacers and M3 screws.
Fig.6. Lower the PCB
together with the front
and rear panels into
the base, ensuring
the panels slide into
the grooves. Four M3
screws fasten the PCB
into place.
Installing MMBASIC firmware
To load the MMBASIC firmware, you will
first need to download the STM32CubeProgrammer software, which is available
from: https://bit.ly/pe-nov21-stm32
This software is free, but STM do require you to have an STM account, or
at least to provide your name and email
address. They will email you a link to
download the software. Then install this
software on your computer (Windows,
Linux and macOS are supported).
You will also need the latest version
of the MMBASIC firmware. Visit https://
geoffg.net/maximite.html and scroll
down to the bottom of the page to download the latest firmware file. Extract the
file, and save it on your computer. (At
the time of writing, the latest version was
CMM2v5.07.01.bin)
With the G2 connected to your computer (via the single USB type-B lead),
ensure that the BOOT jumper link is
positioned on the PRG position (ie, the
left two pins are shorted). Then turn on
the G2 and check the green power LED
lights up – this will indicate that the 3.3V
line is operating correctly. Then press the
Reset button (S2 – located near the VGA
socket) which will put the STM32 into
firmware programming mode.
Next, run the STM32CubeProgrammer
software on your computer. On the top
right of the program window select UART
as the communications method. If the
program does not automatically recognise
the UART connection, click on the small
blue circle to the right of the Port drop
down list to refresh the entry.
Click on the ‘Connect’ button. You
should then see a series of messages
finishing with the message ‘Data read
successfully’. Any messages in red will
indicate an error.
Click on the download button on the
left side of the STM32CubeProgrammer
window and the software will switch to
the ‘Erasing and Programming’ mode.
Use the ‘Browse’ button to select the
firmware file (it will have an extension
of .bin). Tick the ‘Verify programming’
checkbox. Finally, click on the ‘Start
Programming’ button.
The STM32CubeProgrammer software
will then program the firmware into the
Flash memory of the STM32 (the STM32CubeProgrammer software calls this
‘downloading’). After a short time, a dialog box will pop up saying ‘File download completed’. Do not do anything at
46
this point as the software will then start
reading back the firmware programmed
into Flash. When this has successfully
completed, another dialog box will pop
up saying ‘Download verified successfully’. The whole operation will take
around a minute – and remember, any
messages in red will indicate an error.
Once the firmware has been successfully installed, disconnect the G2 from
your computer, and set the jumper-link
on the BOOT header to the RUN position
(right-two pins shorted). It is now time
to carefully insert the CR1220 coin cell.
Initial testing
Now for the moment of truth – testing
your G2 powers up successfully. Connect
your 5V PSU along with a VGA monitor, and a USB keyboard (to the top USB
port). Use the front panel power switch
to turn the G2 on, and after less than a
second, you should see the Maximite
logo and the version number of the firmware that you have just loaded. If your
monitor remains blank, ensure that you
have not left the BOOT jumper link in
the PRG position.
Note that depending upon your monitor, it may take longer than one second
for an image to appear (the VGA signal
will however be outputted from the G2
within one second of powering up). The
delay is purely the time it takes for your
monitor to ‘sync’ to the VGA signal; I
have one ‘branded’ monitor that takes
eight seconds, and a TV that is instant.
The first time the G2 is powered up, it
will ask for the keyboard layout – press
1 for UK (other language options will be
listed). Then it will request the date and
time – simply enter the relevant numbers as guided.
If nothing appears to happen when
you press a key, it may be because the
USB keyboard you’re using is not fully
compatible – simply try another one. I
prefer to use a Logitech K400+ wireless
keyboard (costs around £30) since it is
nice and compact, and it has never failed
me during many hundreds of CMM2
tests. There is another bonus to using the
aforementioned keyboard (or any other
wireless keyboard for that matter). When
hooked up to a large TV the G2 can be
comfortably used from the sofa!
At this point, it is worth performing
another power test (especially if you fail
to see anything on the monitor). If you
disconnect the monitor and keyboard,
you should see a current draw of around
200mA. Any excessive deviation from
this means you’ll need to go back and
check things over
Testing the SD socket
Before mounting the PCB into the case,
there are a couple of quick tests to perform.
With the monitor and USB keyboard connected, insert an SD card (ideally a branded one with a capacity between 8GB and
128GB). Power down, and after a couple
of seconds, power back up. This time you
should see the command prompt appear
immediately (without requests for the
keyboard layout or the date and time options). If it does ask for these items again
then the chances are that the battery is
either missing, incorrectly located, or flat.
With a fresh battery correctly mounted,
these options are retained whenever the
G2 is powered down (ie, the main USB
5V power is removed).
Now check in the very bottom-right
corner of the display for the correct date
and time. If not correct, then you can
use the DATE and TIME commands to
amend this (see the CMM2 User Manual
for more details).
Next, eject the SD card (by gently pushing it in to release the internal latching
mechanism), and in the bottom-centre of
the screen you should see a ‘Check Disk’
message appear. Re-insert the SD Card
and make sure the message disappears.
If ‘Check Disk’ remains on the screen
no matter whether an SD card is inserted
or not, then ensure that the solder joints
on the SD socket’s three side pins are not
shorting to the main body of the socket.
If everything is working up to this point,
we can move onto the final step.
Mounting the PCB
The case used for the G2 is the same compact one that has been used for all Colour
Maximites. It comprises two main body
parts, the base (which has four mounting
Practical Electronics | November | 2021
pillars built in), and the lid. The G2 PCB is
mounted in the base, and four 5mm spacers
are added between the PCB and the pillars,
as shown in Fig.5. These pillars raise the
PCB and the connectors so that they will
match the cut-outs in the front and rear
panels. The pre-cut front and rear panels
need to be positioned over the connectors
before lowering the PCB down so that the
panels slide into the grooves cut into the
base (see Fig.6). This will then line up the
four PCB holes with the four pillars and
spacers. To save your sanity, it is worth
using a small piece of Blu Tack under each
spacer to avoid them falling off the pillars
when lowering the PCB into place.
Use four M3 screws to fasten the PCB
securely into place but do not over-tighten them. Finally, slide the lid down into
position by ensuring the panels line up
with the lid’s grooves, and use the two
longer case screws to hold the case together securely. This results in a professional-looking assembled unit.
Parts list 1 (SMDs on part-assembled PCB)
Resistors
All 0805 unless otherwise indicated
2x 2.2Ω R42, R69
1x 10Ω
R44 (1206)
2x 75Ω
R11, R22, R33
21x 120Ω R1, R7-10, R12, R18-21, R23, R29-32, R35, R43, R50, R56, R58, R62
27x 240Ω R2-6, R13-17, R24-28, R34, R45, R53-55, R57, R59-61, R63-65
3x 1kΩ
R36, R37, R68 (1206)
5x 4.7kΩ R49, R72, R73, R80, R81
13x 10kΩ R38-41, R46-48, R51, R52, R66, R67, R70, R71 (1206)
Capacitors
All 0805 unless otherwise indicated
2x 6pF
C12, C13
2x 12pF C42, C43
32x 100nF C2-4, C10, C14, C15, C17-20, C22-39, C44-47 (1206)
2x 1µF
C6, C16 (1206)
2x 2.2µF C7,C9 (1206)
1x 4.7µF C40 (1206)
4x 10µF C1, C5, C8, C41 (CASE-A_3216)
2x 100µF C11, C21 (CASE-D_7343)
Welcome Tape
Now that you have finished assembling
your G2, you are probably keen to see
what it can do. To get you started, we
recommend the Colour Maximite 2
Welcome Tape. This was curated by
Thomas Williams, and it comprises a
collection of programs written by the
user community. These include games,
demonstrations and utilities. It has an
easy-to-use menu, and you can always
press CTRL-C to break out of a program
and then LIST its code to see how it
works. Download the Welcome Tape
here: https://bit.ly/pe-nov21-maxwel
Semiconductors and crystals
All one-off
STM32H743IIT6
IC3 (LQFP-176) processor
CH340G
IC8 (SOIC-16) USB driver
MT48LC16M16A2 IC4 TSOP54 SDRAM
DS3231MZ
IC7 (SOIC-8) RTC
AMS1117
REG1 (SOT-223) 3.3V LDO
32.768kHz
X1 (SMD-3215_2P) crystal
8MHz
X3 (SMD-7050) crystal oscillator
16MHz
X2 (SMD-CRY-3225_4P)
LED
LED2 (0805)
Keeping up to date
Parts list 2 (kit)
It’s well worth regularly visiting Geoff
Graham’s website (https://geoffg.net/
maximite.html) for links to review websites, and other sites of interest for both
the CMM2 and CMM2 G2. Also keep an
eye on whether you have the latest version of the MMBASIC firmware from
this same link. If you wish to upgrade
the firmware, then simply download the
relevant .bin file, connect your G2 to
your computer (via a single USB lead),
and move the G2’s BOOT jumper link to
the PRG position. Press the small reset
button and use the STM32CubeProgrammer software as outlined above to download the .bin file into the STM32. Once
installed, move the BOOT jumper link
back to RUN. Then, on power-up, check
that the new firmware version number is
displayed in the start-up screen.
Finally, there is a great community on
The BackShed Forum that discuss all
topics related to Maximites and Micromites. if you have any questions, then
this is a good place to seek answers. The
link to this friendly forum is: https://bit.
ly/pe-nov21-bshd
Practical Electronics | November | 2021
Switch
Tactile Switch
S2 (SMD-SW-4_5.1x5.1x2.5) Reset Switch
All one-off unless otherwise indicated
Part-assembled PCB
IR remote receiver, Vishay TSOP4838/40 (IRD1)
3mm dual LED assembly, Dialight 553-0112F (LED1)
SD card socket, Hirose DM1AA-SF-PEJ(72) (CON6)
3.5mm stereo socket, Switchcraft 35RASMT4BHNTRX (CON4)
Right-angle vertical PCB-mount SPDT toggle switch (eg, RS 734-7107) (S1)
Coin cell holder, HARWIN S8411-45R
15-pin VGA socket (CON5)
40-way, 2 row, right-angle PCB header, 2.54mm pitch. Hirose
HIF3F-40PA-2.54DS(71) (CON3)
USB V2.0 type-B connector Amphenol FCI 61729-0010BLF, power (CON2)
Dual USB type-A PCB socket, Amphenol ICC 72309-8034BLF
CR1220 3V lithium battery
Multicomp Pro G738 case 140x110x35
Front panel
Rear panel
2x 3-way header 0.1-inch pitch (JP1, JP2)
2x Jumper link (0.1-inch slide on)
4x 5mm nylon spacers
4x 8mm M3 bolt
Next month, we will add the optional
USB mouse controller chip if you want to
use a USB-protocol mouse with the G2.
Until then, have fun!
Questions? Please email Phil at:
contactus<at>micromite.org
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