QTERM-R55 User's Manual
21
QSI Corporation Fax 801-466-8792 Web www.qsicorp.com Phone 801-466-8770
The EIA-485 interface uses intelligent electronics to con-
trol the direction of the interface (transmit vs. receive). The
interface is held in receive mode until the user application
transmits data. The circuit senses the beginning of the
transmission and immediately switches to transmit mode
until the transmission is ended. At that time, the interface
reverts to receive mode until another transmission is
requested. All of this is handled by the interface electronics,
and is completely transparent to the user application. This
can simplify the task of writing software for the EIA-485
interface, because the application does not need to directly
control the direction of the interface.
The QTERM-R55 operating system does not specify or
enforce any protocol or link layer functions on the EIA-485
interface. This must be provided by the user application.
Most EIA-485 networks use some form of master-slave
protocol to control network traffic. This is accomplished in
software by adhering to a few simple rules:
1)
Slave devices must never initiate a transmis-
sion unless they are queried by the master.
The slave then needs to respond within a cer-
tain time period.
2)
Master devices may initiate transmissions to
slaves, but after doing so the master should
wait (and not transmit again) until the slave
has responded or the timeout period for the
slave response has expired.
3)
If broadcast queries (which require a
response from multiple slaves) must be sup-
ported, the slaves should respond sequen-
tially or otherwise resolve the response
traffic to avoid contention.
3.5
LCD Display
The QTERM-R55 display is a 4-line by 20-character
supertwist LCD unit. The entire 128-byte ASCII character
set can be displayed; also, many Greek letters, katakana
characters, non-English alphabetic characters and math
symbols can also be displayed.
Appendix B. is a chart which shows how the QTERM-R55
will display each 8-bit value. Note that the ASCII portion
of the chart (the first 128 characters) is similar, but not
identical, to the true ASCII chart shown in Appendix A.
If you ordered the backlight, the qaBASIC commands
listed in Chapter 2 will allow you to turn the backlight on
and off. Without the backlight, these commands have no
effect.
3.6
Keypad
The QTERM-R55 is available with a 24-key or a 40-key
keypad. The Power-On Setup menus allow you to control
both key click (on or off) and key repeat (on or off, delay
and rate).
3.7
Other Options
3.7.1
Speaker Option
The QTERM-R55 includes an audio speaker which is used
for key beeps and for beeping in response to a beep or bell
command.
3.7.2
Real-Time Clock Option
If you order the real-time clock option, the QTERM-R55
includes hardware support for the
date$
and
time$
qaBASIC commands.
3.7.3
Switching Regulator
The standard QTERM-R55 uses a switching regulator
which allows the terminal to be powered from a 8-volt to
32-volt DC source.
User's Panel
4 places
Cut Out This Hole
4 mm max radius
183
170
Figure 3-7. Cutout Dimensions for the QTERM-
R55 Large Character Panel-Mount Terminal.
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