Operation mode setting circuitry for microprocessor

Claim 2

Operation mode setting circuitry for a microprocessor operable in any one of a plurality of operation modes, the operation mode setting circuitry comprising: a terminal for receiving an analog voltage the voltage level of which serves for designating one of the said plurality of operation modes; an analog to digital converter, connected to the said terminal for converting the voltage level of the analog voltage into a corresponding digital signal; and a decoder means connected to said analog to digital converter for decoding the digital signal and for generating therefrom a signal for setting the microprocessor in that one of the operation modes corresponding to the voltage level of the analog voltage.

Claim 3

Circuitry as claimed in claim 1, wherein the decoder means comprises a register circuit connected to the analog to digital converter for storing the digital signal, and a mode decoder circuit connected to the register circuit for decoding said digital signal stored in the register circuit.

Claim 4

Circuitry as claimed in claim 2, wherein the decoder means further comprises an edge detector circuit for detecting an edge of a reset signal for initializing the microprocessor, and at least one AND gate circuit, the or each AND gate circuit having a first input terminal, a second input terminal and an output terminal, the or each first input terminal being connected to a detection output of the detector circuit, the or each second input terminal being connected to the analog to digital converter, the or each output terminal being connected to the register circuit, the said digital signal being applied to the register circuit via the AND gate circuit or circuits when the microprocessor is initialized by the reset signal.

Claim 5

Circuitry as claimed in claim 1, 2 or 3 wherein the analog to digital converter is a sequential comparison type analog to digital converter.

Claim 6

Circuitry as claimed in claim 4, wherein the analog-to- digital converter comprises a voltage comparator arranged for comparing the said analog voltage with a reference voltage, a voltage generator and selector circuit which generates a plurality of voltages and selects one of those voltages for delivery to the voltage comparator as the reference voltage, a digital value generator circuit, providing a digital value, which when the comparison output of the voltage comparator indicates non-coincidence of the said analog voltage and the reference voltage, is operable to change the digital value and to provide a signal which causes the voltage generator and selector to select another of the said plurality of voltages as the reference voltage, and which, when the said comparison output indicates coincidence of the said analog voltage and the reference voltage, delivers the digital value as the said digital signal.

Claim 7

Circuitry as claimed in any preceding claim, wherein the digital signal comprises a plurality of bits.

Claim 8

Circuitry as claimed in any preceding claim, integrated in the same chip as the microprocessor, wherein the said terminal is a single input pin of the chip dedicated for operation mode setting use.

Claim 9

A microprocessor chip incorporating circuit 14 as claimed in any preceding claim.