| ??? 10/04/04 05:21 Read: times |
#78664 - RE: Simplified and working schematic Responding to: ???'s previous message |
Why the extra step of the 26-pin DIP connector to the DB25 male connector? Because I can't get any stinkin' DB25 male connectors to solder onto the PCB anywhere in the entire city of Monterrey Mexico. You could use a DB25 male connector with solder cups (for soldering wires to it) and clamp the edge of PCB between the two rows of solder cups. Then you can solder the solder cups to according solder pads of PCB. Imagine, the male connector is sitting on the edge of PCB, if you hold the PCB vertically. Looking again at the parallel port pinout I'm now observing that I've only connected pin 25 of the DB25 to ground. Considering what you suggested about using a ground every other line, may I assume it would be appropriate to go ahead and connect the other 7 ground lines on the DB25 to ground as well? Yes, this would be advantageous, as your cable is 1.5m long. The additional ground wires would act as a shield, decreasing the danger of cross coupling. Another positive effect would be the relevant decrease of ground noise between your AT89S8285 and PC motherboard, just due to decreased ground impedance between both partners. Nevertheless, the use of this single 220 Ohm resistor in buffered MISO line (printer cable), as you have drawn it in your schematic, is still very useful, as it provides you with a series termination. Connect the resistor directly to according buffer output pin. It's always wise to at least use series termination, when running digital signals over cables. It even helps to minimize EMI. Now you might ask, what to do with the other lines? Well, here the PC motherboard provides the needed series termination resistors. Kai |
