FlexNet driver documentation
PTT signalling using Soundcard/DSP drivers
There seems to be some confusion on how drive PTT with my Soundcard and DSP driver. So here are some instructions on how to do it.
Standard PC Soundcards
Note: The MIDI port must be MPU401 compatible. Old Soundblaster models have a proprietary MIDI port which cannot be used to generate a PTT signal.
Personal Sound Architecture (PSA) Soundcards
Texas Instruments TMS320C26 and TMS320C50 DSP Starters Kits (DSK)
DG1SCR DSP Board
Note: newer versions of the DG1SCR monitor program use the RTS line for hardware handshaking, therefore RTS is no longer available as PTT signal.
Analog Devices EZKIT Lite
The following signals are available at the parallel port:
The following signals are available at the serial port:
MIDI out is the output of the serial midi interface, which runs at 31500 baud. The DSP does not output anything if PTT is off (level is inactive high) and it keeps sending zero-bytes during PTT on (format is 8 data bits, 1 start bit and 1 stop bit). The MIDI out can be found usually at the game port connector, pin 12 (TTL levels), ground is found at pins 4 and 5 and +5V is found at pins 1 and 8. Since MIDI out does not deliver a constant level at PTT, one must use a retriggerable monoflop with about 5ms impulse duration. It has to be triggered on the falling edge.
Please note that the Vox circuitry should only be used for 1200 baud AFSK. It is not well suited for 9600 baud FSK
You must adjust the output level of the right channel to the highest possible volume in order to have enough signal voltage to turn on the MOSFET transistor.