Re: Parallel port hardware


"Jon Slaughter" <Jon_Slaughter@xxxxxxxxxxx> schreef in bericht
news:A7CNi.412$sm6.247@xxxxxxxxxxxxxxxxxxxxxxx

Placed a printerport schematic on ABSE.

Also see you point for communicating with PGDx. You will need to keep the
printer control line high as long as the PGDx can go into outputmode. If
not you can get a collission and too high a current in the circuit. That
old 7406 could sink a lot of current but one cannot know about the modern
integrated printerports. Guess you do not know about the PGDx either.
(Guess it's not open collector as you would not have a problem if it
was.) So you will need that serial resistor for current limiting. Ever
saw some type of electronic collission detection but it is too late to
look after it now.

petrus bitbyter




You will need to limit the current somehow because sometimes both outputs
will happen happen to be active at the same time


Yes, this is the main problem. Sure I can program it so its high through
the programming but I'd rather not take that chance in general. I'm not
quite sure how to handle this. The problem is with the pic though. I could
add a resistor to limit the current but then it will reduce the voltage.
Although it might not matter to much.

I send an schematic to alt.binaries that shows the idea I'm looking at.

Thanks,
Jon.


Did not find the collission detection but I think the circuit below will
prevent any output to be blown providing the level shift you need at the
same time.

----+-------+-----+--5V
| | | --+---+--2.5V
.-. .-. | | |
| | 10k| | | .-. .-.
| | | | | | | | |
'-'4k7 '-' | 10k| | | |56k
| | | '-' '-'
| | |\| | |
| +---|-\ ___ | | PIC
SPP | | | |-----|___|--+--)---+------
----+-+-----)---|+/ 2k7 | | I/O
control| | |/| | |
| | LM339 | |
| | | | |
| | | /| | |
| | | /+|--+ |
+-----)-----)-------| | |
| | \-|-----+
| | \| |
| | LM339 |
.-. | .-.
| | | | |
10k| | | 10k| |
'-' | '-'
| | |
| | |
------------+-----+----------------+---------
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Any PIC I/O pin I am aware of can sink and source at least 1mA. So the 2k7
resistor being the maximum load will prevent damage from I/O current. At the
same time, the input leakage current on a PIC input pin is in the uA range.
So the 56K will prevent the input to become floating when the output goes
tri-state. Some PICs can activate weak pull ups to do the same.

petrus bitbyter


.

Relevant Pages

  • Re: Parallel port hardware
    ... Also see you point for communicating with PGDx. ... keep the printer control line high as long as the PGDx can go into ... serial resistor for current limiting. ...
    (sci.electronics.design)
  • Re: Parallel port hardware
    ... petrus bitbyter pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx posted to ... Also see you point for communicating with PGDx. ... keep the printer control line high as long as the PGDx can go into ... serial resistor for current limiting. ...
    (sci.electronics.design)
  • Re: Parallel port hardware
    ... Also see you point for communicating with PGDx. ... keep the printer control line high as long as the PGDx can go into ... Did not find the collission detection but I think the circuit below ...
    (sci.electronics.design)
  • Re: Parallel port hardware
    ... Also see you point for communicating with PGDx. ... printer control line high as long as the PGDx can go into outputmode. ... So you will need that serial resistor for current limiting. ...
    (sci.electronics.design)