Constant speed portamento

DETAILED DESCRIPTION In copending application Ser.
No.
603,776 entitled "Polyphonic Tone Synthesizer", there is described a musical tone generating system in which any one of a plurality of tone generators is assigned to a note when a key is actuated.
As each key is actuated on the instrument, data identifying the note and the key assignment status is stored in a Read/Write assignment memory.
A suitable circuit indicated at 14 in FIG.
1, for sensing the condition of the keys storing such information is described in U.
S.
Pat.
No.
4,022,098, entitled "Keyboard Switch Detect and Assignor".
Once a key is assigned to a note generator, the pitch of the note is determined by a voltage controlled oscillator in the assigned tone generator in response to the note information stored when the key is actuated.
The manner of controlling the frequency of the oscillator for each tone generator is described in detail in the above-identified application Ser.
No.
634,533, filed Nov.
24, 1975.
The present invention, while not specifically limited to an instrument incorporating the features of the above-identified patent applications, is described herein in the preferred embodiment as a modification to such a system.
Portions of the circuit described herein which are common to the circuits described in the above-identified copending applications are identified by the same reference numbers.
Referring to the drawing in detail, the numeral 82 refers to an assignment memory which stores a plurality of control words, one for each tone generator of the polyphonic system.
It is assumed for the purposes of the present disclosure that one tone generator is permanently assigned to the portamento mode of operation and therefore one control word in the assignment memory 82 is always associated with the dedicated portamento tone generator.
When operating in the portamento mode only the upper keyboard is used and only a single note at a time can be played.
In other words, when operating in the portamento mode, the upper keyboard is restricted to monophonic operation