A circular dial buffer is implemented in appropriate random access memory
(RAM) accessible by a DSP for the purpose of storing DTMF digits to be
generated and output on, e.g., a telephone line. To the processor, the
DSP appears to behave much like an off-the-shelf stand alone touch tone
dialer, with the exception that the DSP does not have access to a keypad
input. Instead, in addition to speed dial capabilities, mimicked keypad
input is transmitted by a controller to the DSP rather than timing
information. Thus, instead of requiring the input of rows and columns or
other information relating to button activation on a connected keypad to
input touch tone digits, the principles of the present invention allow
mimicking of keypad input using commands sent by the controller to the
DSP, e.g., a first command indicating that a mimicked, manually operated
key is being pressed, and a second command indicating that the mimicked
key has been released. Thus, the processor in a processor/DSP telephony
system is no longer required to send precisely timed start/stop commands
at precise intervals for directing the timing of a DTMF generator
implemented in the DSP. Instead, touch tone digit commands may be sent by
the processor to the circular dial buffer in the DSP as fast as the
processor-to-DSP interface will permit. Accordingly, the present
invention provides for the generation of DTMF tone signals from a DSP
either based on pre-programmed timing parameters for automatic dialing,
but also in accordance with mimicked keypad activity transmitted from the
controller to the DSP to affect a true DTMF dialer in the DSP.