Specifications

Chapter 7 – SocketModem ISDN (MT128SMI)
Multi-Tech Systems, Inc. Universal Socket Hardware Guide for Developers (S000342F) 112
Electrical Characteristics
3.3V Serial SocketModem ISDN
3.3VDC Characteristics (TA = 0° C to 70° C; VDD = 3.3V ± 0.3V) VDDMAX = 3.6V
Inputs Input High Input Low
–DTR (40), –TXD (35), –RTS (33) Min 2.0V Max 0.8V
–RESET (24) Min 2.0V Max 0.8V
RX+, RX- (S/T Interface Receive) Min 90mV Peak
Normal Mode
Min 220mV Peak
Sleep Mode
Input Capacitance
15 pF
Outputs Output High Output Low Current Drive
–DCD (39), –CTS (38), –DSR (37)
–RI (36), –RXD (34), TCLK (11), RCLK (12)
Min 2.4V Max 0.5V 3.2mA,
7.0mA for TXD
TX+, TX- (S/T Interface Transmit) 1.17V peak @
6mA RL= 50 ohms
5V Serial SocketModem ISDN
5VDC Characteristics (TA = 0° C to 50° C; VDD = 5V ± 0.25V) VDDMAX = 5.25V
Inputs Input High Input Low
–DTR (40), –TXD (35), –RTS (33) Min 2.0V Max 0.8V
–RESET (24) Min 2.0V Max 0.8V
RX+, RX- (S/T Interface Receive) Min 90mV Peak
Normal Mode
Min 220mV Peak
Sleep Mode
Input Capacitance
15 pF
Outputs Output High Output Low Current Drive
–DCD (39), –CTS (38), –DSR (37)
–RI (36), –RXD (34), TCLK (11), RCLK (12)
Min 4.0V Max 0.5V 3.2mA,
7.0mA for TXD
TX+, TX- (S/T Interface Transmit) 1.17V peak @
6mA RL= 50 ohms
Application Notes
Safety Warning Telecom / ISDN-ST
This device is for connection to the ISDN S/T side of an ISDN NT1 device only.
Interface Connector Contact Assignments
Pole (contact) assignments for 8-pole connections (plugs and jacks; i.e., RJ-45)
Function I.430 Polarity Optional Polarity Pole Number
TE NT
3 Transmit Receive + +
4 Receive Transmit + –
5 Receive Transmit – +
6 Transmit Receive – –
ISDN Interface
Termination Resistors: When operating as a TE in point-to-point mode, termination resistors are also required.
However, when configured as a TE in passive bus arrangement, only one TE has these termination resistors.
Note: The MT128SMI ships with a transformer/choke module on it; and therefore, extra EMC filtering on the S/T
interface should not be necessary. Extra filtering may actually degrade the ISDN pulse shape and put the unit
into nonconformity with
I.430.