Siemens SIMATIC NET SINAUT ST7 System Manual page 237

LED displays of the MD2
The following table summarizes the meaning and activity of the six LEDs on the front of the
modem.
Table 6-10
LED no.
1
2
3
4
5
6
The ONL and RI labels have no significance for the MD2.
Front view of the MD2 with removed front panels
The following figure once again shows the front view of the MD2 modem, here, however, the
front panels have been removed to show the connectors located behind them.
SINAUT ST7 Station control system - System Manual
System Manual, 05/2007, C79000-G8976-C178-06
Meaning and activity of the LEDs on the front of the MD2
Labeling Description
TXD Transmit data
The LED flashes in rhythm with the data flow sent to the modem by the
terminal device (TIM) over the RS-232 or RS-485 interface.
RXD Receive data
The LED flashes in rhythm with the data flow sent by the modem to the
terminal device (TIM) over the RS-232 or RS-485 interface.
DTR Data terminal ready
Indicates the status of the DTR signal of the connected terminal (TIM). As
soon as a TIM has started up, it sets its DTR signal to 1 so that the DTR
LED on the MD2 modem is lit continuously.
RTS / ONL Request to send (RTS)
Indicates the status of the RTS signal of the connected terminal (TIM).
When a TIM wants to turn on the transmitter of the modem, it sets its
RTS signal to 1. As long as RTS is set to 1, the RTS LED is lit on the
MD2 modem. The LED goes off as soon as the TIM deactivates the RTS
signal.
CTS / RI Clear to send (CTS)
When the transmitter of the modem has been turned on by RTS, the
modem signals back to the terminal (TIM) that it is clear to send by
setting its CTS signal to 1. As long as CTS is set to 1, the CTS LED on
the MD2 modem is lit. The LED goes off as soon as the TIM deactivates
the RTS signal and turns off the transmitter of the modem.
DCD Data carrier detect
The DCD LED goes on as soon as the MD2 modem detects an adequate
receive level over its receive channel. It goes off when the receive level is
no longer detected.
Installing and putting a SINAUT modem into operation
6.4 MD2 dedicated line modem
237