DN174 - 10Mbps Multiple Protocol Serial Chip Set: Net1 and Net 2 Compliance by Design

10Mbps Multiple Protocol Serial Chip Set: Net1 and Net2
Compliance by Design – Design Note 174
David Soo
Introduction
With the increase in multinational computer networks,
comes the need for the network equipment to support
different serial protocols. When the designer becomes
occupied with the details of the interface specification,
there is always the possibility that one small detail will
be missed. This compliance headache causes designers
to seek out a cost-effective, integrated solution.
The LTC ®1543, LTC1544 and LTC1344A have taken the
integrated approach to multiple protocol. By using this
chip set, the Net1 and Net2 design work is done (see
Figure 1). In fact, Detecon Inc. documents compliance
in Test Report No. NET2/102201/97. With this chip set,
network designers can concentrate on functions that
increase the end product value rather than on standards
compliance.
Figure 1. The LTC1543, LTC1544 and LTC1344A Multiple
Protocol Serial Chip Set
Review of Interface Standards
The serial interface standards V.28 (RS232), V.35, V.36,
RS449, EIA-530, EIA-530A or X.21 specify the electrical
characteristics of each signal, the connector type, the
transmission rate and the data exchange protocols. In
general, the U.S. standards start with RS or EIA and the
equivalent European standards start with V or X. The
single-ended standard, V.28 (RS232) has a lower data
rate than the other differential standards. The current
maximum RS232 data rate is 128kbps. As for the V.35,
V.36, RS449, EIA-530, EIA-530A and X.21 standards,
the maximum data rate is 10Mbps.
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2/98/174_conv
Typical Application
Like the LTC1343 software-selectable multiprotocol transceiver, the LTC1543 and LTC1544 use the
LTC1344A for switching resistive termination. The
main difference between these parts is the functional
partition: the LTC1343 can be configured as a data/clock
chip or a control-signal chip using the CTRL/CLK pin,
whereas the LTC1543 is a dedicated data/clock chip
and the LTC1544 is a control-signal chip.
Figure 2 shows a typical application using the LTC1543,
LTC1544 and LTC1344A. By just mapping the chip pins
to the connector, the design of the interface port is
complete. The chip set supports the V.28 (RS232), V.35,
V.36, RS449, EIA-530, EIA-530A or X.21 protocols in
either DTE or DCE mode. Shown here is a DCE mode
connection to a DB-25 connector.
The mode select pins M0, M1 and M2 are used to select the interface protocol, as summarized in Table 1.
There are internal 50μA pull-up current sources on the
mode select pins, DCE/DTE and the INVERT pins. The
protocol may be selected by plugging the appropriate
interface cable into the connector. The mode pins can
be routed to the connector and are unconnected (logic
1) or wired to ground (logic 0). If all the mode-select
pins are not connected (logic 1), the chip set enters the
no cable mode in which the chip set lowers the supply
current to less than 700μA and three-states the driver
and receiver outputs, and the LTC1344A disconnects
the termination resistors.
Table 1. Mode Selection
Mode Name
Not Used
EIA-530A
EIA-530
X.21
V.35
RS449/V.36
V.28/RS232
No Cable
M2
0
0
0
0
1
1
1
1
M1
0
0
1
1
0
0
1
1
M0
0
1
0
1
0
1
0
1
C6
C7
C8
100pF 100pF 100pF
3
8
11
12
13
LTC1344A
VCC
5V
1
CHARGE
PUMP
2
4
+
+
2
25
C5
1μF
C2
1μF
27
26
C4
3.3μF
D1
6
RXC
D2
7
R1
9
SCTE
R2
10
TXD
11
12
13
NC
VCC
14
R3
20
15
19
12
18
24
17
11
16
2
15
14
1
D2
R1
R2
R3
R4
9
11
12
13
14
RXD A (104)
RXD B
RXC A (115)
RXC B
TXC A (114)
TXC B
SCTE A (113)
SCTE B
TXD A (103)
TXD B
SGND (102)
SHIELD (101)
DB-25 FEMALE
CONNECTOR
26
5
25
13
24
6
23
22
CTS A (106)
CTS B
DSR A (107)
DSR B
D3
10
NC
9
7
D1
8
LL
17
21
LTC1544
28
1
VCC
VEE
27
2
VDD
GND
7
RTS
22
DCE/DTE
6
DTR
16
M2
5
DCD
3
23
M1
4
DSR
16 15 18 17 19 20 22 23 24 1
M0
3
CTS
9 10
D3
8
TXC
5 4 6 7
VCC
24
5
RXD
VEE
M0
C1
1μF
+
28
M1
C3
1μF
VCC
DCE/DTE
3
+
+
LTC1543
M2
14
22
8
21
10
20
20
19
23
18
4
17
19
16
18
DCD A (109)
DCD B
DTR A (108)
DTR B
RTS A (105)
RTS B
LL A (141)
D4
M0
INVERT
15
NC
M1
M2
DCE/DTE
M2
M1
M0
DN174 F01
Figure 2. Controller-Selectable Multiple Protocol DCE Port with DB-25 Connector
Data Sheet Download
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