PAGE 618 AUG 2003 MAN0700-03
b. Using the CGM750 with an OCS for programming (Default Configuration)
The CGM750 modem is pre-configured at the factory for connection to an OCS programming port, so the
OCS can answer calls received from a remote PC running the Cscape programming software.
For this reason, the default factory modem init string is AT&D0&K0S0=1Q1, which causes the modem to
ignore its DTR input, turn off handshaking flow control, enable auto-answer after one ring, and turn off
result codes.
If these default configuration settings are incorrect for your application, they can be modified using any
terminal program. Simply type in the appropriate modem commands to modify the modem settings as
required. For example, to enable result codes, type ATQ0 into the terminal program. When the modem
has been reprogrammed as desired, type AT&W0 into the terminal program to store the settings in
retentive memory. The CGM750 supports the standard AT modem command set. Contact Technical
Support for full details on the AT modem command set.
c. Using the CGM750 with an OCS for real-time data exchange
The default settings will not work if OCS modem INIT, DIAL or ANSWER ladder function blocks are used
to initialize, dial out or to answer a call from another OCS. If the OCS is using the modem in this way,
modem result codes must be enabled (via the ATQ0 modem command).
When a positive edge occurs at the power flow input to an OCS modem INIT, DIAL or ANSWER function
block, first the +++ escape sequence is sent to the modem to force it into command mode, then the
ATE0S0=0V0X0&C1&D2 init string is sent to the modem, followed by the appropriate additional INIT,
DIAL or ANSWER modem command, as programmed into the function block.
The ATE0S0=0V0X0&C1&D2 init string tells the modem: don’t echo, don’t auto-answer, produce numeric
/ simple result codes, indicate connection by activating the DCD output, and hang up if the DTR input
becomes inactive. Unfortunately, the V0X0 portion of the init string does not override the default Q1
setting, so the user must either pre-configure the modem with ATQ0 or must employ a SEND function
block in ladder to send the ATQ0 string to the modem, prior to activating any modem function blocks.
Note: When using a SEND function block to send commands to the modem, AT commands must
end with a carriage return character, which has a decimal value of 13.
d. Using the CGM750 with an OCS for both programming and real-time data exchange
If the OCS is connected to a CGM750 for programming, and also needs to periodically exchange real-
time data with another OCS (or other device) using the same port, the OCS ladder program should
perform the following in ladder. (Also, refer to Items b and c for additional informal.)
1. Activate an OPEN function block to open the serial port in the desired mode.
2. Activate a SEND function block to send ATQ0 to the modem.
3. Activate INIT, DIAL and/or ANSWER modem function blocks to establish a connection with
another device for data exchange.
4. Exchange data via SEND, RECV and/or MODBUS function blocks.
5. De-activate the DIAL or ANSWER modem function block to hang up the phone.
6. Activate a SEND function block to send ATQ1S0=1 to the modem.
7. Activate a CLOSE function block to close the serial port.
8. The serial port and modem are again ready to receive calls from Cscape.
