Datasheet
9
LTC1546
Figure 15. V.28 Driver Propagation Delays
Figure 16. V.28 Receiver Propagation Delays
V
IH
V
IL
1.3V
0.8V
1.7V
2.4V
t
PHL
V
OH
V
OL
A
R
t
PLH
1546 F16
3V
0V
1.5V
0V
–3V
3V
1.5V
0V
3V
–3V
t
PHL
t
f
V
O
–V
O
D
A
t
PLH
t
r
1546 F15
SR =
6V
t
f
SR =
6V
t
r
SWITCHI G TI E WAVEFOR S
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Overview
The LTC1546 and LTC1544 form a complete software-
selectable DTE or DCE interface port that supports the
RS232, RS449, EIA530, EIA530-A, V.35, V.36 and X.21
protocols. Cable termination is provided on-chip, elimi-
nating the need for discrete termination designs.
A complete DCE-to-DTE interface operating in EIA530
mode is shown in Figure 17. The LTC1546 half of each port
is used to generate and appropriately terminate the clock
and data signals. The LTC1544 is used to generate the
control signals along with LL (Local Loopback).
Mode Selection
The interface protocol is selected using the mode select
pins M0, M1 and M2 (see Table 1).
For example, if the port is configured as a V.35 interface,
the mode selection pins should be M2 = 1, M1 = 0, M0 = 0.
For the control signals, the drivers and receivers will
operate in V.28 (RS232) electrical mode. For the clock and
data signals, the drivers and receivers will operate in V.35
electrical mode. The DCE/DTE pin will configure the port
for DCE mode when high, and DTE when low.
The interface protocol may be selected simply by plugging
the appropriate interface cable into the connector. The
mode pins are routed to the connector and are left uncon-
nected (1) or wired to ground (0) in the cable as shown in
Figure 18. The internal pull-up current sources will ensure
a binary 1 when a pin is left unconnected.
The mode selection may also be accomplished by using
jumpers to connect the mode pins to ground or V
CC
.
When the cable is removed, leaving all mode pins uncon-
nected, the LTC1546/LTC1544 will enter no-cable mode.
In this mode the LTC1546/LTC1544 supply current drops
to less than 500µA and the LTC1546/LTC1544 driver
outputs are forced into a high impedance state. At the
same time, the R2 and R3 receivers of the LTC1546 are
differentially terminated with 103Ω and the other receiv-
ers on the LTC1546 and LTC1544 are terminated with
30kΩ to ground.
APPLICATIO S I FOR ATIO
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