Podex -- 68HC12 BDM interface pod -

Podex -- 68HC12 BDM interface pod -- Hardware
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Podex, 68HC12 BDM
Hardware
❍ Schematics
❍ Construction
■ "Printed" circuit board
■ List of components
❍ Firmware flashing
Firmware (program inside podex)
Software
Example application
FAQ
Hardware
[ •esky ]
Schematics
To connect a wire on one side and RS232 on the other to the MCU is almost as difficult as to connect a bulb to battery in a torch.
Schéma zapojení podexu
RS232 signals TxD, RxD, RTS, CTS (in schematics marked from podex' point of view) are connected to AVR MCU via buffer U2, MAX232.
In prototype, there has been used "worse" variant MAX232 (no A suffix), which may require 1uF capacitors around it (on PCB the size 1206
was chosen). Thay can be tantalum, but they are also available in ceramic with this capacity (wow, that progress... on Taiwan they are really
working hard). Connector K1 can be plugged directly to the COM-port of IBM PC. LEDs D1, D2 acts as indicators of activity and error state
and also can be controlled by software of control computer. There are signals MOSI, MISO and SCK of serial programming interface of AVR
and its /RESET signal available on connector K3, which serve (together with GND potential from K1 or K2) as an interface for programming
FLASH of AVR by podex firmware. PCB allows connecting a switch S1 for resetting AVR, but this shoudln't be needed. Clock for AVR is
obtained from crystal X1 with the most desirable frequency of 9.216MHz -- maximal supported rate for 5V AT90S2313 is 10MHz and
9.216MHz is the nearest lower rate, which allows precise division to 115200b/s serial transfer. Crystal is connected through point J1, which
should be disconnected and then get clock from external source via connector K2, for example from EClock signal of HC12 CPU. Connector
K2 is to be connected to BDM, and among this external clock contains three-state signal BDM(BKGD), signal /RESET and software
controlled lines MODA, MODB, allowing use of extended memory (bus) of HC12 CPU.
Construction
Podex has been designed on two-sided PCB with SMD components mounted on both sides. The most narrow distance between conductors is
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Podex -- 68HC12 BDM interface pod -- Hardware
cca. 0.2mm, but some very kind people at one PCB laboratory, which officialy supports only spaces greater than 0.25mm, made boards of
podex in a perfect quality. Board has to be put to a cover of two connectors Canon DB9. It is placed between pins of these connectors and
surface soldered to these pins (which are ordinary used for soldering with cable wires). Connectors are used this way to hold a board in
position. Connector K1 is female, according to RS232 connection, K2 is male to avoid their swapping. LEDs are round with 3mm diameter, if
they will be used, it would be very nice to drill holes for them in a cover. As a programming connector K3 I have used SIL (single-in-line)
sockets, available as a line, which can be broken to smaller pieces. Pay attention for this component not to be too much thick to fit in a cover.
J1 can be hardly connected by a wire, if you won't use external clock (otherwise, let it disconnected). You will pobably never need a S1
switch. If you can't use PCB of this layout or you can't order fabrication of it, you can build the circuit on a universal PCB -- it is very simple.
"Printed" circuit board
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PCB (upper layer)
PCB (lower layer)
components placement (upper side)
components placement (lower side)
board layout in Gerber format and CNC drill coordinates
board layout pictures in EPS (zipped) and in one PDF
List of components
ozna•ení
typ
pouzdro
U1
AT90S2313
SO20W
U2
MAX232
SO16
K1, K2
DB9
DB9SM
D1
LED
LED_3mm R
D2
LED
LED_3mm G
C1, C2
CAPACITOR
0805
33p
C8
CAPACITOR
0805
u1
R1, R2
RESISTOR
0805
330
R3
RESISTOR
0805
10k
S1
SWITCH_PUSHBUTTON_NO JUMPER2
X1
CRYSTAL
HC49
J1
JUMPER
JUMPER2
C3, C4, C5, C6, C7 CAPACITOR
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1206
hodnota
9.216MHz
1u
Podex -- 68HC12 BDM interface pod -- Hardware
K3
HEADER3
JUMPER4
Podex box is connected to control computer by direct plugging it to RS232 DB9 connector or by a cable, which must contain signals RTS and
CTS. For BDM interface, there is a standardized 6pin connector, recommended by HC12 documentation, for use of lines MODA, MODB
there is its 10pin extension. Pinout of K2 connector is chosen to allow direct interconnection of self-cutting DB9 connector on the podex side
and 6(10)pin self-cutting connector PFL on the other side of AWG cable.
BDM connectors connection
photo
Firmware flashing
Firmware is loaded to FLASH of AVR AT90S2313 via connector K3. For this it is sufficient to connect serial programming interface signals
to parallel interface LPT/Centronics according to following schematic, widely used in AVR community and known as a "Direct AVR Parallel
Access":
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Podex -- 68HC12 BDM interface pod -- Hardware
Zapojení programátoru AVR p•es LPT
Attention, there should be also conected a ground of podex (GND) to a control computer during programing, using a connector K1. Also it is
needed to power flashed podex by 5V source via K2 connector (it is possible to power it from a HC12 board, if there aren't used lines MODA,
MODB).
With above mentioned parallel port connection there can be used eg. flashing software uisp. The firmware is then loaded eg. by command
uisp -dlpt=0x378 -dprog=dapa --erase --upload --verify if=podex.hex -v=3 --hash=12
(0x378 is LPT base address, podex.hex is filename of the firmware, for more see uisp docs). After loading of firmware the podex is finished
and ready to operate with HC12.
Podex -- 68HC12 BDM interface pod
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http://duch.cz/podex/
Marek Peca, <[email protected]>