Re: [CAD_CAM_EDM_DRO] troubleshooting help

Hi Jerry,

To my knowledge, the 8255 (which I once knew well), hasn't been used for
a parallel printer interface for a LONG time! Most implementations now
are LSI's, and they emulate a buffer for the status, and a latch for the
data and command. The BIOS should take care of anything else. If
options are present in the BIOS for ECP, the parallel port should be
selected for SPP, or "Centronics".

there is also a direction bit, 0x20 on the CMD port, and this bit should
be cleared. Dave's included test program should help.

Also, one should insure that it's the FEMALE DB25 connector, and not a
MALE DB25 SERIAL connector that one's plugged into on the PC!

Is this an add in card? Is it jumpered? If one runs debug (DOS) and
types in D40:0 (enter), the LPT port addresses are at 40:8. I'd watch
before, and after the card is plugged in (power off when changing the
card), and observe if a 278h or 378h in the list of three LPT's comes or
goes. Are there more then one LPT port on the PC?

HTH!

Alan KM6VV


Carol & Jerry Jankura wrote:

>
> Alan:
>
> I don't know how this fits into the equation, but you'll remember that the
> first printer ports used an 8255 parallel port interface chip. In addition
> to the three ports that you mention, this port was at either $37B or $27B.
> It allowed you to program the other ports. As I recall, ports $378 and $379
> could be programmed as either input or output ports, while the port at $37A
> could be split between input and output (the upper and lower halves of the
> port could be either input or output). Now, the current printer port is, I
> believe, integrated with a bunch of other functions. Does it still mimic a
> complete 8255? If so, does it make any sense to program the chip? Is it
> possible to get at all twenty-four pins that the 8255 originally supported?
>
> -- Jerry
>
> |The CMD port is at +1, IE, 889.
> |
> |The bit assignments are:
> |
> |#define CMD_MASK 0x1B
> |
> |#define SPP_STROBE 0x01 /* I nStrobe (pin 1) */
> |#define SPP_AUTOFD 0x02 /* I nAutoFd (pin 14) */
> |#define SPP_INIT 0x04 /* I nInit (pin 16) */
> |#define SPP_SLC_IN 0x08 /* I nSelectIn (pin 17) */
> |#define SPP_IRQE 0x10 /* I IRQ enab */
> |#define SPP_LISTEN 0x20 /* ? direction */
> |
> |Notice that several pins are inverted, per the CMD_MASK.
> |
> |The motors jump, so yes, you have motor power. I suspect you are using
> |the wrong port address, try the others. Also, are you using step/dir?
> |or 4-phase drivers?
> |
> |Sending a 1, 0, 1, 0... sequence to the DATA port (888) should result in
> |pin 2 going alternately high and low. Either put in a delay between
> |OUT's, or wait for a key from the keyboard. THis way, you'll be able to
> |see the changes on the multimeter or LED.
> |
> |Sending a 2, 0, 2, 0... sequence to the same port should result in pin 3
> |going alternately high and low.
> |
> |Sending 1, 0, 1... sequence to 889 (CMD port) should result in pin 1
> |toggleing.
> |
> |PORTS:
> |
> | 888 (378H) data
> | 889 (379H) cmd
> | 890 (37AH) status
> |
> | 632 (278H) data
> | 633 (270H) cmd
> | 634 (27AH) status
> |
> |Try these tests, and then we can advise you better!
> |
> |HTH
> |
> |Alan KM6VV
>
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