Tip #1. Fully study and understand the LPT parallel protocol. There are
books by Que and others that will explain the LPT architecture.

Tip #2 Understand that LPT interfacing won't work with NT/2000/XP without a
LOT of  driver headaches.

Tip #3 Know that there are several serial EEPROM programmers out there. Are
you sure you want to make one from scratch?

Answer to #1 - This all depends on your particular hardware printer port.
Early PC's had fixed i/o lines. Data were output only, handshake were
bi-directional. Later computers had the data lines programmable for i/o.
Even later motherboards had different mode configuration(s) EPP, ECP,
anticipating uses other than printers....... As I stated above, you will
need to be proficient in understanding all the different types and, if this
is going to be just a project for you, or if you are going to design this
into a product.

Answer to #2 - Serial port will be more universal and a little more
forgiving if hooked up wrong, but will involve serial to parallel (and
back) conversion. Not really a big problem. Could be handled within the uC
with some efficient code. From that point on, the uC can probably handle
the actual EEPROM reading and writing.

Answer to #3 - I'd recommend the serial port for compatibility to PC OS. If
you can right good code, a 16F876/877 will finish out the hardware,
although there's going to be a good bit of code in your PC too.

Simple design???? depends on your perseverance.
Good Luck - Rick



Milan Pavlica YU7XW wrote:

> Hello!
> I am going to start to design a simple serial EEPROM programmer for LPT
> port.
> Due that i have never design anything with LPT port i need a few tips..
> 1. Is there pins on LPT port that can be on same Input and Output (not
> only I or O)
> 2. So, is better to use LPT port and a mass of logic devices (aka
> 74HC....) or use COM port and some uC device to setup IO lines
> 3. Or, best variant maybe to use LPT port with a few uC and then to get
> a full 40 pin universal programmer :|
> What is best choice to use?
> THANKS!
> p.s. Didnt i say "simple design" :)

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