Scor­pio News

The audio circuitry allows a selection of one of four inputs and the A/D can be set to read the direct input, true RMS or Log RMS. The maximum input voltage is limited to about 8 volts peak to peak but there is also 50 dB of switchable input gain for lower level signals.

The D/A output is routed through a digital attenuator device which allows 88 dB of attenuation to be inserted in steps of 0.375 dB. Both A/D and D/A run at 40 kHz and therefore the available frequency range approaches 0-20 kHz but the software allows for effective sampling rates lower than this to be used. There is also an additional off-line digital attenuator which is directly controlled from the Z80 via the B side of the PIO.

I have referred to this as a “board” but it is in fact two boards mounted together to give an 8 x 8 inch sandwich. The card that plugs into the 80-BUS holds the TMS, memory, interface and an RS 232 port for direct access to the TMS for de-bugging. The daughter board carries the A/D and D/A devices, the audio circuitry and a set of DC to DC power supplies to generate the various voltages required for the analogue circuitry. The digital board is in fact self-contained and could be used by itself for fast processing of data if the audio circuitry is not required.

The software at present has been written with the specific project in mind and the facilities available in the on-board EPROM are:

• input sampling at variable rate
• waveform replay including a built-in sine wave output
• modulated waveform replay
• swept waveform replay
• white noise (equal energy in all frequencies)
• pink noise (white noise with 3 dB/octave roll off)
• saw tooth or ramp output
• operation as an audio delay line of up to about 1.25 seconds

In addition there is the facility to download any other program into the TMS and to execute it. We have only just taken delivery of the final boards and although we have had the opportunity to experiment with the prototype we have not really come to terms with what it is capable of. We have however already discovered that we have a very powerful tool at our disposal and we are looking forward to developing further applications for it.

If by any odd chance anyone out there is interested in further details of such an esoteric board or would just like to maintain contact with an 80-BUS and MultiNet user they are welcome to contact me. ●