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. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 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 www.linear.com Linear Technology Corporation For applications help, call (408) 432-1900 dn174_conv LT/TP 0298 340K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 1998