23: MODEM MODE
23-6 OPENNET CONTROLLER USER’S MANUAL
When the dial command has been completed successfully, internal relay M8062/M8092 is turned on. If the dial command
fails, internal relay M8072/M8102 is turned on.
The dial command is determined successful when the DCD signal is turned on.
Note: When the OpenNet Controller is powered down while the telephone line is connected, the telephone line is discon-
nected because the DTR signal is turned off. This method should not be used for disconnecting the telephone line. Always
use M8053/M8083 to disconnect the telephone line as described below.
RS232C Port Communication Protocol
Before the telephone line is connected in the modem mode after power up, the RS232C port 1 or port 2 can only send out
an AT command by turning on a start internal relay M8050-M8056 or M8080-M8086. The communication protocol for
the RS232C port after the telephone line is connected is selected by the value stored in data register D8203/D8303.
When the telephone line is disconnected, the RS232C port restores the state as before the telephone line is connected,
whether D8203/D8303 is set to 0 or 1.
When using a TXD or RXD instruction in the user communication mode while the telephone line is connected, insert
internal relay M8077/M8107 (line connection) as an input condition for the TXD or RXD instruction. After the telephone
line is connected, make sure of an approximately 1-second interval before executing the TXD or RXD instruction until the
telephone line connection stabilizes.
Note: When the OpenNet Controller is stopped while the telephone line is connected, the RS232C port protocol changes to
the maintenance protocol even if D8203/D8303 is set to 1 (user protocol in the on-line mode); then the telephone line
remains connected. When the OpenNet Controller is restarted, the user protocol is enabled again.
Disconnect Mode
The disconnect mode includes only one command to disconnect the telephone line. To disconnect the telephone line, turn
on internal relay M8053/M8083. The telephone line is disconnected by turning off the DTR signal since the initialization
string includes the &D2 command.
While a modem command is executed, another command cannot be executed. If two or more start internal relays are
turned on simultaneously, an error will result and error code 61 is stored in modem mode status data register D8211/
D8311 (see page 23-8).
When the disconnect command has been completed successfully, internal relay M8063/M8093 is turned on. If the discon-
nect command fails, internal relay M8073/M8103 is turned on.
The disconnect command is determined successful when the DCD signal is turned off.
After the telephone line is disconnected, the RS232C port restores the state as before the telephone line is connected
whether D8203/D8303 is set to 0 or 1 so that the RS232C port can be controlled by turning on a start internal relay
M8050-M8056 or M8080-M8086.
AT General Command Mode
When the modem mode is enabled, data registers D8230-D8244 or D8330-D8344 are allocated to the AT command string.
Before turning on start internal relay M8054/M8084 for the AT general command mode, store an AT command string in
data registers starting with D8230/D8330. One data register stores two characters: the first character at the upper byte and
the second character at the lower byte in the data register. Use the MACRO instruction on
WindLDR to set the AT command
string and execute the MACRO instruction before turning M8054/M8084 on.
Example of AT Command: ATE0Q0V1
AT and are appended at the beginning and end of the AT general command string automatically by the system program
and need not be stored in data registers. To program the AT command string of the example above, store the command
characters and ASCII value 0Dh for to data registers starting with D8230.
D8203/D8303 RS232C Port Communication Protocol in the On-Line Mode
0 (other than 1) Maintenance protocol
1 User protocol
CR LF
LF
CR
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