Theory of Operation
Serial Port 2 (COM2)
Serial ports 1 and 2 are identical in features and programming with
respect to RS-232-C communication, with one exception. You can
disable serial port 2 by removing jumper W66. This is useful for
systems adding a modem card at the same I/O address as on the
ZT 8809A. After removal of jumper W66, the ZT 8809A no longer
reserves the I/O addresses 2F8 - 2FFh for the on-board serial port, and
allows STD bus devices to reside here.
To connect serial port 2 to an external device, insert optional cables
ZT 90014 or ZT 90027 into frontplane connector J2. Each type of
cable then connects to the IBM PC or compatible as previously
described for COM1.
In addition, RS-422/485 compatible drivers and receivers allow serial
port 2 to communicate as an RS-422 or RS-485 device. Refer to
Appendix A, which describes jumpers W14-W19, W21, W22, and
W29-W32. You may also refer to Appendix A for the description of
W13, and to Chapter 9 regarding shared signals at the printer port if
requiring software control of the RS-485 driver enable. The various
serial communications protocols are discussed here to help solve any
questions regarding protocol selection.
Four Electronic Industries Association (EIA) standards are used for
most serial communications. The major differences between the four
standards are shown in Table 3-2. The RS-232-C standard is designed
for low data transfer rates between a single transmitter and a single
receiver over short distances. The RS-423-A standard increases the
number of receivers and the transmission length but because of a
single-ended implementation, still has low data transfer rates. The
RS-422-A standard implements a differential transmission medium to
support all the features of RS-423-A and a much higher transfer rate,
and is supported by the ZT 8809A. The RS-485 standard, supported
by the ZT 8809A, is similar to RS-422-A with the added ability to
handle multiple drivers and many more receivers.
3-6
Содержание ZT 8809A
Страница 15: ...Tables Table B 9 J5 Pin Assignments B 17 Table B 10 J6 Pin Assignments B 18 Table B 11 J7 Pin Assignments B 19...
Страница 334: ...Jumper Configurations W49 W48 A W47 B A B W37 W66 A W50 B C J7 W67 Figure A 11 W37 W47 50 W66 W67 Jumper Blocks A 34...
Страница 346: ...Jumper Configurations W61 W60 W62 W63 W64 A B A B W65 Figure A 13 W60 W65 Jumper Block A 46...