DS1487 Datasheet, PDF (5/8 Pages) National Semiconductor (TI) – Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver

Parameter Measurement Information (Continued)
*Note: Non Terminated, Open Input only
FIGURE 12.
DS012920-13
*Note: Non Terminated, Open Input only
FIGURE 13.
DS012920-14
Pin Descriptions
Pin I/O
#
1O
2I
3I
4I
5 NA
6 I/O
7 I/O
8 NA
Name
RO
RE (Note 1)
DE
DI
GND
A
B
V_CC
Function
Receiver Output: If A > B by 200 mV, RO will be high; If A < B by 200 mV, RO will be low. RO will
be high also if the inputs (A and B) are open (non-terminated).
Receiver Output Enable: RO is enabled when RE (Note 1) is low; RO is in TRI-STATE when RE
(Note 1) is high.
Driver Output Enable: The driver outputs (A and B) are enabled when DE is high; they are in
TRI-STATE when DE is low. Pins A and B also function as the receiver input pins (see below).
Driver Input: A low on DI forces A low and B high while a high on DI forces A high and B low when
the driver is enabled.
Ground
Non-inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
Inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
Power Supply: 4.75V ≤ V_CC ≤ 5.25V
Applications Information
The DS1487 is a low power transceiver designed for use in
RS-485 multipoint applications. The DS1487 can transmit
data up to 2.0 Mbps based on a ratio of driver transition time
to the unit interval (bit time) of 10%. This maximum data rate
may be further limited by the interconnecting media. The
DS1487 provides a ¹â„4 unit load to the RS-485 bus across the
common mode range of −7V to +12V. This allows up to 128
transceivers (¹â„4 unit load) to be connected to the bus. The
DS1487 also guarantees the driver’s output differential volt-
age into a worst case load that models standard termination
loads and 32 unit loads (=128 DS1487’s) referenced to the
maximum common mode voltage extremes. With a minimum
of 1.5V swing into this load, a 1.3V differential noise margin
is supported along with the standard common mode rejec-
tion range of the receivers.
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