Instruction manual

Page 20
Appendix
External Modem Mode
For correct operation in external modem mode, the kV RSX requires that the operating mode
jumpers be positioned correctly, an external modem be connected to the communications cable
and the setup strings and baud rate be correct for the modem. At the time of power up, the kV
RSX initializes the external modem. If the modem is not present or the set up strings or baud
rate are incorrect, the kV RSX will continue to try to configure the modem. The Modem
Configuration Error bit, in the End Device Mode and Status table of the kV RSX, will be set if the
kV RSX cannot properly configure the external modem.
kV RSX Setup Strings
In External Modem Mode the kV RSX has programmable setup strings which serve to: reset the
external modem device to a known state, initialize it for communications with the kV RSX, setup
call answering and call origination configuration parameters.
External Modem Reset String
The kV RSX is designed to interface with many different external modem devices both domestic
and foreign using telephone or wireless technologies. Because there is no common method of
resetting these various external modems to a known state, the kV RSX provides a programmable
reset string.
Connecting the kV RSX to an external telephone modem will require the use of a 9 pin female to
25 pin male D-sub adapter such as Inmac part #37101 or Global Stock No. THC4496.
Before putting the kV Meter into service it is important to know the reset string and reset state of
the external modem device connected to the kV RSX. The majority of external modem devices
can be reset to their user programmed state by the string "ATZ". This 'z' is the default reset
string value for the kV RSX. Some modems have several user programmed profiles, in which
case the Z is appended with a number to load the desired profile.
Most modems can be reset to their factory default state by "AT&F". If this is the case and the
factory state is desired the 'z' should be reprogrammed with "&F". Some modems have several
factory default profiles, in which case the &F is appended with the number of the desired state.
Some wireless modems only emulate the telephone modem AT command set and do a good job
of resetting themselves on power up. Sending an AT reset command to these modems may
start an undesired, lengthy channel reacquisition process. In these cases it may be best to
program the reset string to all blank characters. This will prevent the kV RSX from sending a
reset string.
In configuring the external modem device to work with the kV RSX it is important to know what
resets the modem and what the reset state is.
Initialization String
The programmable kV RSX initialization string is used to set the external modem to a
configuration required by the kV RSX to control the modem. There are six (6) main functions
that are programmed through the initialization string. These are listed below along with the AT
command that sets the desired configuration in popular telephone modems.