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RS232 computer vs laptop + pcmcia

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kyndal

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Im having some problems with rs232 from my laptop.
i have heard that serial ports on laptops arent 100% native..
okay nothing to do about that..

But i recently i "hacked" an old ibm modem, inspired by this page
https://www.electricstuff.co.uk/diyserial.html

i used a standard rs232 transiever (ADM211) fro analog devices (what i had lying around)

But! even with this standard tranciever, supplyied with 5v and uses 0.1 uf
it seems i am unable to program a pic with my developmentboard?
Why is this, shouldent this be a standard native rs232?

the hack works 100% i can sync my Palm Vx, and ipaq..

Any hints?

/Kyndal
 

robotman

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What you might be seeing is that your target device (PIC system) is trying to extract power from the lines.

The ADM211 (and several of the lower power single chip RS-232 devices) that use the 0.1uF cap can not deliver the required power.

The way the single chip RS-232 works is that there are three charge pumps. One 5 to 10V, one 5 to -5, and one -5 to -10 (I think the sequencing is right). Anyway, the earlier parts all used 10uF caps. This allowed for more current extraction durring the off times of the charge pumps.

Anyway, on most PCs, they have access to +12V and -12V. This is used to power a very inexpensive interface chip providing the proper signalling. The the +12V and -12V are on the main supply, sufficient current is always present (unless limited somewhere).

Although this might not be your problems, it is something to be aware of.

robotman
 

kyndal

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power from the lines! maby,, the board itselve has a seperate 5 voltage supply, but i belive that the pic needs higher programming voltages!..

could it be posible to fix my pcmcia card by using a maxim chip insted, with 1.0uf or 10uf (what part??)
they still need to pump it from the 5v in the pcmcia card!
and somehow fit the big caps inside the card!!! ?

can i use 10uf with the existing transiver insted og 0.1?

could i change my pic board, regarding the powersupply,
(some transistor on the programming lines, and higher voltage?)


OR!
maby i could make a small box, with 12 voltage external supply (or smart smps solution from 5v)
that does a
RS232 (from computer) -> TTL and back to RS232 but using a "native" or better transiever?
Any thoughts on this?
what tranciever should be used?

this device would make it posible, finally to use your laptop for this sort of thing?

/Kyndal
 

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