ZyXEL Communications U-336R/RE manual Flow Control, Fax Operation

The basic AT commands ATV0 and ATQ1 do not affect the above CONNECT and DISCONNECT status report result codes. The modem will always return the same status format as above.

Flow Control

In extended fax AT command mode, your modem always uses hardware (CTS/RTS) flow control. The flow control signaling used sending a fax is:

∙CTS is used by your modem for DTE flow control. When the modem turns CTS off, the buffer inside the modem is full and cannot accept any more data. The computer should send data only when CTS is ON.

∙RTS is used by the computer to signal your modem that the fax message is finished. As soon as RTS off is detected, the modem starts the post message handshaking to make sure that the remote facsimile has received the fax message successfully. Then it hangs up the phone and sends a status report to the DTE.

If you want to send a multi-page fax, just add the RTC signal between the fax message of each page. The modem detects the RTC signal automatically, handshakes the multi-page procedure with the remote facsimile and sends the next page.

The following flow control signaling is used while receiving a fax:

∙CTS is not used when receiving fax.

∙RTS is used to inform your modem that the computer cannot accept data at this moment. The modem will not pass received data to the DTE if RTS is turned off.

When finished receiving the fax message, your modem will turn off CD then send a status report result code to the DTE.

74 Fax Operation