QRP Labs QCX-mini, Руководство по сборке

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4.14 Optional GPS interface
The GPS was a late addition to the design. It is added to facilitate several useful features:

Calibration of the 27MHz reference oscillator

Calibration of the 20MHz system clock

For WSPR, discipline of the frequency (drift correction)

For WSPR, setting and discipline of the real time clock

For WSPR, setting the Maidenhead Locator square
The optional GPS interface is provided by the same connector as the paddle (Serial, PPS
and Ground); +5V is available at the tip connection of the PTT connector. The QLG1 GPS
receiver kit is ideal for the QCX-mini. However other GPS modules could also be used. The
following requirements of the GPS module must be met:

Positive-going (leading edge) 1 pulse per second signal with a reasonable pulse
width – e.g. some older GPS module have a 1us pulse and this will not be long
enough. The QLG1 GPS receiver provides a 100ms (0.1s) duration pulse, though
shorter pulses would also work.

9600 baud serial data sending standard NMEA 0183 GPS sentences

“TTL” voltage levels i.e. 0V “low” and 5V “high” (or at least, below 1.5V and above
3.5V)
The GPS is therefore wired directly in parallel with the paddle. The GPS may not be used at
the same time as the paddle. This would cause the transmitter to be keyed by the 1pps and
serial data signals.
Always put the kit into Practice Mode (see menu 4.7) before
connecting a GPS, to avoid accidentally frying the PA.
The ATmega328P has a USART serial data peripheral. However, the pin assignments were
already made, so far down the design process, at the time the GPS receiver option was
included. Furthermore, the I/O pin availability was already scarce. So, the two GPS signals
share the same I/O as the paddle inputs. A software-emulated USART peripheral module
now reads the GPS serial data, at 9600 baud.
If you connect a GPS and forget to put the kit in practice mode, it will automatically
recognize serial data at the paddle input and temporarily enable practice mode (an ‘A’
appears in the display) to protect the PA circuit.
QCX-mini assembly Rev 1.05_Fr
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