Meinberg GPS169PCI, Operating Instructions Manual

Page: 9 / 34

9
Asynchronous serial ports
Two asynchronous serial interfaces (RS232) called COM0 and COM1 are available
to the user. Only COM0 is available at the rear panel slot cover, COM1 must use
another submin-D connector which can optionally be connected to the 5 pin jumper
block on the board. The monitoring program can be used to configure the outputs. In
the default mode of operation, the serial outputs are disabled until the receiver has
synchronized after power-up. However, they can be configured to be enabled imme-
diately after power-up. Transmission speed, framing and mode of operation can be
configured individually for each port. Both of the ports can be configured to transmit
either time strings (once per second, once per minute, or on request with ASCII ´?´
only), or to transmit capture strings (automatically when available, or on request).
The format of the output strings is ASCII, see the technical specifications at the end
of this document for details.
Time capture inputs
The board provides two time capture inputs called User Capture 0 and 1 (CAP0 and
CAP1) which can be mapped to pins at the 9 pin connector at the rear panel. These
inputs can be used to measure asynchronous time events. A falling TTL slope at one of
these inputs lets the microprocessor save the current real time in its capture buffer.
From the buffer, an ASCII string per capture event can be transmitted via COM1 or
displayed using the monitoring program. The capture buffer can hold more than 500
events, so either a burst of events with intervals down to less than 1.5 msec can be
recorded or a continuous stream of events at a lower rate depending on the transmissi-
on speed of COM1 can be measured. The format of the output string is described in the
technical specifications at the end of this document. If the capture buffer is full a
message "** capture buffer full" is transmitted, if the interval between two captures is
too short the warning "** capture overrun" is being sent via COM1.
Pulse and frequency outputs
The satellite clock's pulse generator outputs TTL level pulses once per second
(P_SEC) and once per minute (P_MIN). A DIL switch on the board can be set up to
map one or both of the pulses to pins at the 9-pin connector at the rear slot cover.
A TTL level master frequency of 10 MHz is derived from the TCXO. By default,
this frequency is available only at the 5 pin jumper block on the board.
In the default mode of operation, the pulse outputs are disabled until the receiver has
synchronized after power-up. However, the monitoring program can be used to enable
these outputs immediately after power-up.