Retrofitting a printer port

A project log for V-Tech Genius Leader / PreComputer Hacking

Turning a toy into a hardware tinkering platform

Bernhard Bernhard "HotKey" Slawik 10/28/2019 at 19:144 Comments

Since many owners of models that don't have a printer port pointed out: There are some unpopulated parts on their main PCB and asked if the printer port could be retro-fitted.

Well, I guess so!

So there are only 8+1 bits in the OUT direction and a single bit in the IN direction. The latter is used to tell if a printer is connected and ready.

As I have found out, it is also used for PC communication: Using the 8 data output bits, the notebook selects, which bit of the incoming byte it wants to be set on Pin 11. So I guess the PC-Link cable contains an 8-bit "AND" IC.

But enough chatter: Here is the list of missing parts for the printer port:

Component IDMarkingsDescription
<IC>P9506AN / DM74LS244N
74LS244N Octal Buffer
<Connector>Ribbon cable to D-SUB 25Ribbon 1-9 to Pin 1-9
Ribbon 10 to Pin 11
Ribbon 11 to Pins 18...25 and Shield
(where Ribbon 1 is near C93)
C1240340 nF capacitor
C93222 AEC2.2 nF capacitor
R35, R41, R42, R43, R44brown black orange10k resistors
Q10LM90 /  14C / M[otorola] 521NPN transistor
Q11LM90 / 15 C / M[otorola] 512PNP transistor

Please let me know if you find any mistakes. Also, drop me a line if you managed to pull off the upgrade procedure. I'd love to hear about it!

Happy upgrading!


Evan Allen wrote 11/02/2019 at 02:17 point

can you verify that r44 is 10k as well, it's behind a wire in your picture.  I'd also like to know which jumpers are not connected on yours and what the pinout of those transistors is.  

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Bernhard "HotKey" Slawik wrote 11/02/2019 at 18:23 point

Oh, didn't see R44 was missing as well. Yes, I can confirm that it's also a 10k. I corrected the log. Thanx for pointing out!

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Evan Allen wrote 11/05/2019 at 14:31 point

ok, it works, I used a PN101 transistor for the LM9014 npn and a pn2907 for the LM9015 pnp.  I also had to restore all the jumper links except the one in your picture under the '244 that isn't connected.  I can now print to a dot matrix printer, but only using the german rom from mame (presumably from you).  I put it on a w49f002 which is pin compatible with the mask rom and it boots just fine.  I also got the US rom dumped and it'll be in MAME soon.  the gl4000 MAME driver doesn't currently emulate the printer port properly but hopefully it will soon (the data bus is shared with the keyboard matrix and the strobe/busy lines are some bits at the memory address of the beeper).  I also hope to have the LPRINT and LLIST commands restored to the US rom soon.  I'll have a writeup of all my stuff in a bit.  

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Ken Yap wrote 10/28/2019 at 21:31 point

That would be the Centronics standard, 8 data lines, STROBE and BUSY.

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