DS481 Datasheet, PDF (6/10 Pages) National Semiconductor (TI) – Low Power RS-485/RS-422 Multipoint Transceiver with Sleep Mode

Parameter Measurement Information (Continued)
DS012919-15
*Note: Non Terminated, Open Input only
FIGURE 14. Entering Sleep Mode Conditions (modes and exit parameters shown)
TABLE 1. Device Pin Descriptions
Pin
Name
Description
No.
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.
2
RE
Receiver Output Enable: When RE (Note 1) is LOW the receiver output is enabled. When RE (Note
(Note 1) 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.
7
DO
Driver Output/Receiver Input, 485 Bus Pin.
(Note 1)
/RI
(Note 1)
8
V_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 ¹â„2 unit load and ¹â„4 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 ¹â„2 UL option is available in industrial
temperature and the ¹â„4 UL is available in commercial tem-
perature.
First, for a ¹â„2 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 ¹â„4 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 ¹â„2 UL and ¹â„4 UL devices is the in-
creased number of nodes on one bus. In a single master
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