AXIOMTEK AX10445 Series, Руководство пользователя

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AX10445 Module Series User
’
s Manual
Technical Reference
17
3.2 About EIA RS -422/485
As the constraints on RS -232C extend only up to a distance
of 50 feet, and at speed up to 19200 baud, a better standard
for serial communication was needed. Such requirement
initiated the development of the new RS -422/485 standard
that permits higher data rates and longer cabling distances.
In RS -422/485, the majority of signals specified in RS -232C
were preserved.
The RS -422/485 transmits data through differential signal
lines. These differential signal lines have better noise
immunity. The characteristics of these standards are given in
Table 1 .
Characteristics RS-232C RS-422A RS-485
Mode single-ended differential differential
Maximum number
drivers
receivers
1
1
1
10
32
32
Maximum cable
length
15m 1200m 1200m
Maximum data rate
(bits/s)
20K 10M 10M
Transmit levels
±
5V min
±
15V max
±
2V min
±
1.5V min
Receive sensitivity
±
3V
±
0.2V
±
0.2V
Load impedance 3K to 7K 100
Ω
min 60
Ω
min
Output current limit 500mA to VCC
or GND 150mA to GND 150mA to GND
250mA to –8V
or +12V
Driver Load, min
(power off)
300
Ω
60K 120K
Table 1