Amplicon 485HF9, Инструкция по эксплуатации

Страница: 17 / 25

Model 485HF9
Page 17
3.2.1 Electrical Levels
When checking out serial communications circuits, it is useful to know what signal levels to
expect. The specified voltage levels of RS-232 data and control signals are summarised in the
following table:-
Interchange Voltage –3 to –15 +3 to +15
Binary State 1 0
Data Signal Marking Spacing
Control Function OFF ON
Signal Ground is at 0 volts, and the region between –3 and +3 volts is the transition region.
The Model 485 Adaptor will normally be used in close proximity to the RS-232 port, but in a
case where it is not close, the following limits apply. The electrical levels at which RS-232
operates limit the maximum data rate to about 20 kilobaud (sometimes used up to 100 kBd)
and the maximum cable length between transmitter and associated receiver to about 15 m (50
ft)
3.2.2 9/25 way Adaptors
The wiring list in figure 3.1 shows the necessary connections to adapt a 9 way RS-232 port to a
25 way RS-232 port, or vice versa. Due note should be taken of the gender of the mating
connector, and a gender change can be incorporated in the adaptor if required.
FIGURE 3.1 DTE ADAPTOR - 9 Way to 25 Way
3.3
RS-422/485 Application Notes
RS-422 and RS-485 have very similar characteristics, with RS-485 being compatible with, and
offering all the advantages of RS-422 plus some additional capability. RS-422 pre-dated RS-
485 as a standard, but RS-485 is now more popular and used in new system design. For the
485 Adaptor, the on board circuitry for the two modes is identical, the application deciding the
mode of interface operation.
8 DCD
3 Rx D
2 Tx D
20 DTR
7 SIG GND
6 DSR
4 RTS
5 CTS
22 RI
DCD 1
Rx D 2
Tx D 3
DTR 4
SIG GND 5
DSR 6
RTS 7
CTS 8
RI 9
25 WAY PIN-OUTS 9 WAY PIN-OUTS