Motorola (freescale) MC68705P3 mcu reader / copier / programmer

Note: Reading operates at 4 MHz Speed (Switch I2 in Position 0) in order to divide by 4 the read-out.
If one 68705P3 append to be hard to read then operates at 1MHz Speed.
The extraction of the program is done by consecutive verifications : This task that can take up to 3 days is very reduced owing to a powerful algorithm.
Depending on the memory used in the microcontroller, it can takes from few hours to a dozen of hours.

MC68705P3S reader tool:


The diagram is given here : 68705p3.pdf (49 Kb)
operating manual (french) is given in the file (307Kb)
The microcontroller "1"MC68705P3 must be programmed with the content 68705-1.bin (2Kb) [Ckecksum 18AF] the listing of the program disassembled is given in the file 68705-1.src (47Kb).
The little MS-DOS Software lect-p3 that allow transfering the content of the SRAM 6116 to the P.C. is : (50Ko)

The SRAM 6116 can be replaced by the M48Z02 (or MK48Z02) Zeropowerram from ST , so that it can be read by a universal devices programmer.

The software lect-p3 can also work under WIN98.

This tool is a dedicated reader / copier tool that allow to read out the MC68705P3 mcu.
It is a standalone tool.
Some leds indicates the state of operation.

notice 68705-3.txt

notice 68705-5.txt


how-to-use (spanish)


Put Switch I5 on Position AUTO (0)
Put Switch I2 on position 4 MHz (0)
Plug the power
Put the 68705P3 containing the program to read in the Socket "2"
Put Switch I3 on position 12 Volts (0)
Put Switch I1 on position 5 Volts Operation (1) : Led L1 lights on
Put Switch I4 on Position Lect/Prog (1)
Press the key BP during a second then Led Led blinks every half seconds and led L4 blinks very quickly. Reading is starting , extrcating the program in the SRAM.
At the end of the reading Led L2 L3 stay lit but L4 is lit off
Put I4 switch in position Stop (0)
Put I1 in position Stop (0) Led L1, L2, L3 light off
Put away the MC68705P3 that has been read.


Fix the empty device on socket 2
Put switch I2 on position 1MHz (1)
Put Switch I3 on Position 25Volts (1)
Put switch I1 on Position Operation 5Volts (1) : Led L1 light on.
Put Switch I4 on position lect/Prog (1)
Put Switch I5 on Position Prog (1) : Led L4 blinks every 5 seconds approx. and indicates that programming is in progress during 1mn 30s approx.

At the end of the programming, the led L3 lights on In the case the programm has been transfered all right, Led L2 should light on 1 second after and indicates the verification is OK Led L4 stops blinking.
Put Switch I5 on position Auto (0) : Led L2 & L3 light off
Put I4 on position Stop (0)
Put I1 on Position Stop (0) : Led L1 lights of Remove the programmed 68705P3.


Power Supply : the power supply is done by a 5VA Transformer with 2 voltages 24 Volts and 9 Volts : the power does not exceed 5 Watts approx.

Components side:

Diagram (schematic available here 68705p3.pdf (49 Kb) )

Diagram & Component (better scan version) (269Kb)


on the manual of the kit it is not given
it is said :
press E to write RAM
press R to read RAM
press V to test if 68705p3 is empty
press P to program MC68705P3
press L to read P3
COM1/COM2 choice press O
press Q to Quit the program
led L5(TX) and L6(RX) display the operation on the computer

In order to work to the software lect-p3 you need the following connexion

Use de DB25 to DB9 adaptor if necessary.

DB25 -
(2) TX
(3) RX
(7) GND + Connect (4) & (5) each other ; Connect Also (6) , (8) & 20 each other. this allow the software to recognise if the programmer is plugged or not.

so it means that on the SUB-D9 , pin 7-8 should be connected together and 6,1 and 4 should be connected together

1,4,6 should not be connected to pin 8, but pin8 should be connected to pin 7 ond the SUBD-9 female connected to the serial port of the PC.

Components List

Transformer 5VA 2 outputs : 24 Volts and 9 Volts
Regulator 5 Volts L7805CV
Fuse 1.5A 250V and Fuse socket
Programmed MC68705P3(1) [Checksum 18AF]
Q Crystal 4MHz
2 x 28 pin Sockets , 1 x24 pin Socket ZIF Socket Optionnal
1 SRAM 6116 or ZEROPOWER RAM M48Z02-70PC1 (contains lithium cell 10 years) that can be read by a universal programmer.
CMOS ICs : 4040 x2, 4011 x1
5 SWITCHES ON-OFF 3 connexions
Transistors T2,T3,T4 : BC546
Transistor T1: 2N2907A
L1, L3, L5, L6 3mm Red Led
L2, L4 3mm Green Led
DZ2 BZX85C10 Zener
DZ1, DZ3 BZX85C12 Zener
1N4004 x 8 , 1N4148 x8
R33 :100 OHMS
R4, R5, R28 : 330 OHMS
R29, R30 470 OHMS
R9 : 820 OHMS
R3, R34 : 1KOHM
R10 TO R19, R19 - 21 TO 26 631 - 32 4K7OHMS
R1- R8- R27 22KOHMS
R7 : 27KOHMS
R20 : 100KOHMS
R6: 330KOHMS
C1-C4-C8-C9-C11 100 NF
C3 2.2µF/POL
C2-C5-C10 10µF/POL
C6 100µF/POL
C7 470µF/POL




MC68705P3 reader eagle schematic & PCB (RAR Archive -88 kb)

MC68705P3 reader schematic (PDF- 35Kb)

Bill of Materials (.txt - 8 Kb)

MC68705P3 reader (spanish) (RAR Archive - 2kb)

You can use the circuit to write the 68705-1.bin program. with this steps:

1. copy the 68705-1.bin in 6116 Eprom (AT28C16 for me)
2. I leave Socket 1 empty
3. Socket 2 with UC
4. pin 17 in socket 1 to GROUND
5. I1->5V, I3->25V, I4->Program.
6. pin 19 in socket 1 to +5V
WRITE begins!

How to read MC68705U3 EPROM by Peter Ihnat A method to read the EPROM contents of a programmed MC68705U3/R3

MC68705U3 Bootstrap ROM

MC68705P3 Bootstrap ROM

MC68705P5 Bootstrap ROM ; blank.bin (2Kb-binary file This is a file with all zeros) The Bootstrap ROM doesn't program zeros, it skips them

Motorola MC68705P5 NUM Mode read out


Eagle BRD modified (.BRD compatible Eagle 7.1 - 164Kb) courtesy Tristan Gallop (UK)

Gerber files archive MC68705P3 reader (ZIP Archive - 138Kb)

made the following changes based around the components I was able to obtain at the time...

1. Separate 24v and 9v 2,8VA transformers:
myrra 50/60Hz 2.8VA transformers

2. DF02 bridge rectifiers instead of single diodes:

3. Switch traces modified to suit the "Turbo" switches found in most older PC cases ;)

There are plenty of the push button switches on ebay, I searched for "pcb latching push switch" and lots came up.
I think the ones you need for my PCB have the white button, not the blue but I may be wrong! There is no information about the pin configuration.

I found a blue one at work and it seemed to be set correctly for the original PCB design.

4. 68k resistor added next to R29 to bleed the 24v capacitor when 230v is removed.

The rest of the board and component list is the same as the original design.


assembly notes:

The toggle switches are digikey 450-2099-ND SWITCH TOGGLE DPDT 0.4VA 20V. very expensive. NOTE: these do NOT fit into the layout,You have to widen the holes on the PCB with a larger drill to make them fit

The 4 MHz quartz didn’t start up reliably, sometimes it ran at 8MHz. I drilled a small hole into the pcb besides the quartz and soldered a direct connection from the quartz’s can to GND (see photo). That assures reliable start-up at 4 MHz

R15 and R16 collide with the textool socket, so I had to solder them on the underside of the PCB.

rework the connections on the RS232 plug, so I can use a 1:1 cable. However, I can’t get the software to work, although I was using a true DOS 6.22 computer

the zero-power RAM ST M48Z02 was plugged on an intermediate socket before plugging it into the PCB socket, because

to have some protection of the RAM’s pins from bending

need to solder a 4k7 resistor between pins 24 and 21 directly into the intermediate socket in order to protect the RAM from corrupting its contents when inserting and removing it from the PCB. Also, there is an extra 100nF capacitor and a 4148 diode (see picture) for the same reason

avoid mains transformers and connected the voltages from DC lab supply directly to the regulators.


solder side

If you need a PCB of the MC68705P3 Reader do not hesitate to contact me

Other Resources:

M6805 Index Page



If you look forward for other information about this MC68705P3 Reader, do not hesitate to contact me by e-mail at: .

Si vous recherchez des informations pour ce lecteur de MC68705P3, vous pouvez me contacter par e-mail : . De même si vous avez des informations sur ce programmateur, n'hésitez pas à contribuer à cette page.

Retour au sommaire

Retour à la Page d'accueil

16 mars, 2019