VIEWER(OPCSDEFS) Optical Printer Control System VIEWER(OPCSDEFS)
NAME
viewer - configure the viewer input port and bit mask
USAGE
viewer [port] [mask] [test] [0] # (all values in hex!)
EXAMPLES
viewer 0000 00 00 # No viewer detection
viewer 03bd 40 40 # LPT1 pin 10, HI bit detects condition
viewer 03bd 40 00 # LPT1 pin 10, LO bit detects condition
DESCRIPTION
If your system has a 'viewer open' switch, it can be wired to one of
the IBM parallel ports to allow the software to sense its state, to
prevent exposing film with the viewer open.
[port] is the port number in the range 0000-03ff.
If [port] is 0000, no viewer checking is done.
[mask] is applied to the value received from the port
whenever the software is checking for a viewer open condition.
This is applied before comparing to [test].
[test] is compared to the value read from the port after
[mask] is applied. If the result is the same as [test], a viewer open
condition exists.
WIRING CONSIDERATIONS
Normally you would use an optically isolated interface card for the
buckle and viewer switches, e.g. PIO-100(DOCS).
If directly connecting switches to the parallel port, it is recommended
you use a separate, dedicated 5 volt power supply wired through the
switches in such a way that when the sensing switch is tripped, +5
volts is passed to the computer.
Such a supply can be a store-bought 12 VDC transformer, with an added
7805 5 volt regulator. Note that if you use an unregulated supply (ie.
a transformer without the 7805), the voltage output can vary according
to the AC power from the wall, which normally varies plus or minus
10 percent, causing a wide margin of possible voltages to the
computer's sensing input, which really wants either +5 or ground, and
nothing else.
As with any signal going to the sensing input on a computer, the
signal should never be open..the signal must pull either 5 volts
or ground for a TRUE or FALSE condition. An open input is more like
a radio antenna that will register both TRUE AND FALSE
conditions randomly, causing spurious sensing errors.
To further prevent noise problems, use sheilded wire for the sensing
signals, and ground the shield ONLY at the power supply end. Do NOT
use the sheild as a ground return for the computer..use a separate
conductor for signal ground. Keep wire lengths as short as possible.
If noise problems persist, and you have ruled out a problem with the
computer, it may be that the wire is simply too long for such a low
voltage signal. You may want to use a higher voltage (12 volts) in
the switch circuitry to drive an optoisolator close to the computer,
using the optoisolator to switch 5 volt signals to the parallel port.
You can find the base port value for the parallel ports from the
operating system using the DOS 'debug' utility:
C>debug # run 'debug'
-d40:8 f # enter this (not the '-')
0040:0008 BC 03 78 03 00 00 00 00 # debug spits this out
-q ----- ----- # type 'q' to quit debug
| |
| LPT #2's port base address
|
LPT #1's port base address
Your machine may show different values. In the case above, 03BC
is the base port value for LPT1..note the bytes are in reverse
order in typical LSB/MSB fashion.
See the PARALLEL() man page which shows the pin out and port addresses
of the IBM PC's parallel ports.
BUGS
None.
SEE ALSO
DEENERGIZE(OPCSDEFS) - define port/bit to deenergize motors
ALLSTOP(OPDSDEFS) - define port/bit to detect the allstop key
BUCKLE(OPCSDEFS) - define port/bit to detect film buckles
VIEWER(OPCSDEFS) - define port/bit to detect viewer open
TRIPSWITCH(OPCSDEFS) - define port/bit to detect trip switches
SETBIT(OPCSDEFS) - set bit(s) on a port
CLRBIT(OPCSDEFS) - clear bit(s) on a port
XORBIT(OPCSDEFS) - invert bit(s) on a port
PARALLEL(BIOS) - parallel port pinout with port/bit masks
PIO-100(DOCS) - OPCS Parallel I/O interface board, e.g.
http://seriss.com/opcs/pio-100/
ORIGIN
Version K1.12e+ Gregory Ercolano, Venice California 04/10/98