User's Manual

5. Pin 11 can be used as the hardware reset. Since the input pin is at high impedance,

never fail to tie the input level.

6. It is no problem if Pins 12, 13 and 14 are leaved open.

7. Since the interface is CMOS structure circuit, it is recommended to take a remedy

against ESD problem (e.g. surge absorber; VRD series, made by Ishizuka Denki).

4.2

Serial Interface Setting

For connecting the FDL01TU modem with an external terminal equipment, RS232C is

appropriate for 1 to 1 topology. And set the RS485 mode to make RS485 multi-dropping

topology for multiple equipment connection. Interface configuration can be made with Pin

12 (/RS485ENB) of the serial communication connector.

To configure the RS485 mode, pull down Pin 12 with 10k ohm register. In this case, do

NOT connect this pin DIRECTLY to the GND. This is because in RS485 mode, this pin

will be as an output pin, after the initialization completes, to control the output buffer of the

RS485 driver IC chip. As for the RS232C interface, no connection is required because it is

pulled up inside.

Since the interface level of the FDL01TU modem is CMOS, the level conversion circuit

must be provided outside for connecting it with the RS232C or RS485 interface. For an

example of the level conversion circuit, see p.64 C

ONVERSION

IRCUIT

Figure 4–1: Connection Example to PC

Converter

232C

L modem