Chapter 3 - SSP Installation (XVME-956/400)
PARALLEL PORT USAGE
W20
PC/AT printer port
short
Bidirectional data port
open
Table 3-17 shows how to set this jumper.
Table 3-17. Parallel Port Jumper
When W20 is open, the direction of data transmission can be controlled by a signal (port output enable)
applied to pin 26 of connector J3, or pin 1 of W20. This signal enables data output when low, and data
input when high. O n l y the eight data lines are affected.
A convenient way to generate the port output enable signal is simply to tie J3 pin 26 to one of the
parallel port's output control lines (-STROBE, -AUTOFD, -INIT, or -SEL IN). Whichever line you
use, be sure that your software controls the line in such a way that you get the data direction you
desire.
There are limitations on the total length of cable that can be driven reliably by the ports of the board.
A full discussion of these limitations is beyond the scope of this manual. I n general terms, the
maximum cable length depends on the data rate, and on the amount of noise and interference in the
environment. However, you will almost always have reliable data transmission if you observe the
following restrictions:
• P a r a l l e l Port: Cable length up to 10 feet
• R S -232C Serial Port: Cable length up to 50 feet; data rates up to 19.2K bps
• R S -485 Serial Port: Cable length up to 4000 feet; data rates up to 57.6K bps
3-14
