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PSM-500/500L/500LT SCPC Satellite Modem
Operation
Caution – What is not immediately obvious is that the time set is the time of the "current"
configuration with no carrier before switching to that configuration. Thus if configuration #1
is set to 12 seconds and #4 is set to 2 seconds (all others being set to zero) then when on #4 for
12 seconds with no receive carrier the modem will change to #1, and when on #1 for 2 seconds
with no receive carrier then the modem changes to configuration #4.
Note that all of the above examples would be "safer" if the <Dem: Alarm – CXR Lock> is set to
"Mute and ...". With this setting the transmit carrier is turned off when no receive carrier is
present, even if commanded on.
3.15 Special Control Mechanisms
The PSM-500 modem includes several special controls that were built in for specific customer
systems, but may be of use by other user. This are listed here since they are not considered
normal options and could be easily overlooked.
3.15.1 Power-Up Behavior
The PSM-500 modem has the capability to always revert to the transmit carrier disabled on
power-up. This might be useful for example in mobile environments where the antenna may not
be deployed or aligned on each power-up cycle. Setting this option in the <Modulator: IF Mute>
parameter allows such operation.
In other cases the user may require that the modem always revert to a specific configuration on
power-up. The normal behavior is for the modem to power-up with the last settings still in effect.
One of the options in the Unit Configuration column is "Power-Up" control (<Unit: Config – Pwr-
Up>). The default setting is to "Last" which performs as the normal described above. A user can
select any of the 8 stored configurations to be recalled on each power-up cycle. This could be
useful in a mobile environment or a DAMA system where a "home" channel is desired on each
power-up. In a large system units can be pre-set to a specific configuration for use in initially
bringing up a site and then easily changed to another configuration for normal operation.
3.15.2 Monitors and Outputs
The PSM-500 has always had the ability to send one of 3 measured parameters to an analog
monitor output on the rear panel Alarm connector at pin 5 of J5. A newer monitor output added in
Version 0.47 of the modem code allows putting the Data Interface RTS status onto either the A or
B Alarm relay output, also on the rear panel J5 connection. Since these relays are form C, either
logic direction can be chosen for the output to use in controlling other equipment. Control of this
feature is in the <Intf: I/O – RTS Monitor> parameter. Caution – Setting this to either Alarm A
or B relay will override an other settings going to that alarm relay. It is the responsibility of
the user to set alarms properly when using this unique feature. This relay control is also not de-
bounced with a time delay, therefore a fast changing or chattering RTS signal will cause the relay
to chatter. This feature is independent of the <Intf: I/O – RTS> parameter which can be used to
control the Carrier enable via the RTS status.
3.16 Burst Mode Operation
Note: As of the time of this manual the burst mode is a special factory request option and not
installed in standard modems. The following description is typical of burst operations.
The modulator burst mode is controlled by the interface RTS/CTS and data flag signals. The
sequence of events for the burst mode is as follows:
1. The RTS from the DTE device is normally active. The idle character from the DTE is
a continuous Mark condition. The modulator output carrier is off in this idle state.
PSM-500/500L/500LT - Rev. 0.91
Page 3-41
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