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DS481 Datasheet(PDF) 6 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. DS481
Description  Low Power RS-485/RS-422 Multipoint Transceiver with Sleep Mode
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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DS481 Datasheet(HTML) 6 Page - National Semiconductor (TI)

 
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Parameter Measurement Information (Continued)
TABLE 1. Device Pin Descriptions
Pin
No.
Name
Description
1
RO
Receiver Output: When RE (Receiver Enable) is LOW, the receiver is enabled (ON), if DO/RI
≥ DO
(Note 1)/RI (Note 1) by 200 mV, RO will be HIGH. If DO/RI
≤ DO (Note 1)/RI (Note 1) by 200 mV,
RO will be LOW. Additionally RO will be HIGH for OPEN (Non-terminated) Inputs.
2RE
(Note 1)
Receiver Output Enable: When RE (Note 1) is LOW the receiver output is enabled. When RE (Note
1) is HIGH, the receiver output is in TRI-STATE (OFF). When RE (Note 1) is HIGH and DE is LOW,
the device will enter a low-current sleep mode after 600 ns.
3
DE
Driver Output Enable: When DE is HIGH, the driver outputs are enabled. When DE is LOW, the
driver outputs are in TRI-STATE (OFF). When RE (Note 1) is HIGH and DE is LOW, the device will
enter a low-current sleep mode after 600 ns.
4
DI
Driver Input: When DE (Driver Enable) is HIGH, the driver is enabled, if DI is LOW, then DO/RI will
be LOW and DO (Note 1)/RI (Note 1) will be HIGH. If DI is HIGH, then DO/RI is HIGH and DO
(Note 1)/RI (Note 1) is LOW.
5
GND
Ground Connection.
6
DO/RI
Driver Output/Receiver Input, 485 Bus Pin.
7DO
(Note 1)
/RI
(Note 1)
Driver Output/Receiver Input, 485 Bus Pin.
8V
CC
Positive Power Supply Connection: Recommended operating range for V
CC is +4.75V to +5.25V.
Unit Load
A unit load for an RS-485 receiver is defined by the input cur-
rent versus the input voltage curve. The gray shaded region
is the defined operating range from −7V to +12V. The top
border extending from −3V at 0 mA to +12V at +1 mA is de-
fined as one unit load. Likewise, the bottom border extending
from +5V at 0 mA to −7V at −0.8 mA is also defined as one
unit load (see
Figure 15 ). An RS-485 driver is capable of
driving up to 32 unit loads. This allows up to 32 nodes on a
single bus. Although sufficient for many applications, it is
sometimes desirable to have even more nodes.
The DS481 has 12 unit load and 14 unit load (UL) options
available. These devices will allow up to 64 nodes or 128
nodes guaranteed over temperature depending upon which
option is selected. The 12 UL option is available in industrial
temperature and the 14 UL is available in commercial tem-
perature.
First, for a 12 UL device the top and bottom borders shown in
Figure 15 are scaled. Both 0 mA reference points at +5V and
−3V stay the same. The other reference points are +12V at
+0.5 mA for the top border and −7V at −0.4 mA for the bot-
tom border (see
Figure 15 ). Second, for a 14 UL device the
top and bottom borders shown in
Figure 15 are scaled also.
Again, both 0 mA reference points at +5V and −3V stay the
same. The other reference points are +12V at +0.25 mA for
the top border and −7V at −0.2 mA for the bottom border
(see
Figure 15 ).
The advantage of the 12 UL and 14 UL devices is the in-
creased number of nodes on one bus. In a single master
DS012919-15
*Note: Non Terminated, Open Input only
FIGURE 14. Entering Sleep Mode Conditions (modes and exit parameters shown)
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