Character display system having negative image cursor

Claim 2

In a normally blanked CRT display apparatus for characters that are successively applied to the apparatus for display at a succession of separate address locations thereof: means for generating a succession of unique unblanking bit patterns individually representative of the successively applied characters; means for normally outpulsing the successive bit patterns in serial form to the apparatus to selectively unblank the corresponding address locations; and means rendered effective during the outpulsing of only a selected one of the successive bit patterns for inverting the states of the associated bits to provide a negative image cursor indicating the location of a selected character.

Claim 3

In a CRT display apparatus for alphanumeric characters which are storable in the form of digitally coded data in a plurality of separate locations of a memory and which are cyclically outpulsed from the memory at a clock rate, wherein characters outpulsed from successive locations of the memory are applied to a normally blanked display in a plurality of address locations individually representative of the memory locations and addressed in synchronism therewith, an improved arrangement for visibly marking a selected address location on the display to form a cursor, which comprises: means operative at the clock rate for generating a succession of unique unblanking bit patterns individually representative of the characters stored at the successive locations of the memory; means for normally applying the bits of each generated bit pattern in serial form to the apparatus to selectively unblank the corresponding address location, said location being unblanked when the then-occurring one of the bits is in a prescribed one of two states so that the location is normally defined by a prescribed contrasting pattern on the display; and means rendered effective during the address of the selected location on the dispLay for inverting the bits of the corresponding bit pattern so that the display at the selected address location is locally defined by the negative of the normal contrasting pattern.

Claim 4

In a CRT display apparatus for alphanumeric characters which are storable in the form of digitally coded data in a plurality of separate locations of a memory and which are cyclically outpulsed from the memory at a clock rate, wherein characters outpulsed from successive locations of the memory are applied to a normally blanked display in a plurality of address locations individually representative of the memory locations and addressed in synchronism therewith, an improved arrangement for visibly marking a selected address location on the display to form a cursor, which comprises: means operative at the clock rate for generating a succession of unique unblanking bit patterns individually representative of the characters stored at the successive locations of the memory; means for normally applying the bits of each generated bit pattern in serial form to the apparatus to selectively unblank the corresponding address location, said location being unblanked when the then-occurring one of the bits is in a prescribed one of two states so that the location is normally defined by a prescribed contrasting pattern on the display; and means rendered effective during the address of the selected location on the dispLay for inverting the bits of the corresponding bit pattern so that the display at the selected address location is locally defined by the negative of the normal contrasting pattern.

Claim 5

Apparatus as defined in claim 2, further comprising, in combination, first and second multibit binary counters having a bit capacity at least equal to the number of address locations; means for successively advancing the first counter through increments of one count at the clock rate in synchronism with the outpulsing of successive characters from the memory; and means for independently moving the second counter through a selectable number of counts to control the location of the cursor.

Claim 6

Apparatus as defined in claim 3, further comprising coincidence means for generating a cursor control indication during the clock period in which the counts of the first and second counters coincide.

Claim 7

Apparatus as defined in claim 4, further comprising means rendered effective upon the generation of the cursor control indication for advancing the second counter by one count.

Claim 8

Apparatus as defined in claim 4, in which the inverting means comprises means rendered effective upon the generation of the cursor control indication for reversing the states of the bits in the bit pattern applied to the display during the next clock period.

Claim 9

Apparatus as defined in claim 6, in which the display is provided with an unblanking input, and in which the state-reversing means comprises, in combination, first and second parallel video paths interconnecting the output of the bit pattern applying means and the unblanking input, the outputs of the respective paths being in phase opposition: a first bistable circuit exhibiting a first stable state when a set input thereof is activated and a second stable state when a clear input thereof is activated; mean for enabling the first path when the first bistable circuit is in its first state and for enabling the second path when the first bistable circuit is in its second state; a normally disabled control gate; means rendered effective upon the occurrence of the cursor control indication for conditioning the control gate for operation at the beginning of the next clock period; means operative at the start of said next clock period for momentarily operating the conditioned control gate to activate the set input of the first bistable circuit; and means rendered effective at the end of said last-mentioned next clock period for activating the clear input of said first bistable circuit.

Claim 10

Apparatus as defined in claim 7, in which the conditioning means comprises, in combination, a second bistable circuit exhibiting a first stable state when a set input thereof is activated and a second stable state when a clear input is activated; means for coupling an output of the second bistable circuit to the control gate to condition the latter when the second bistable circuit exhibits its first state; means for activating the set input of the second bistable circuit during the clock period in which the cursor indication is generated; and means for activating the clear input of the second bistable circuit at the end of the next clock period.

Claim 11

Apparatus as defined in claim 4, in which the display has up to 2N M address locations arranged in N lines of M characters each, each of the first and second counters has a 2N M count capacity, and the apparatus further comprises, in combination, means for scanning the address locations in successive lines of the display at intervals of M clock periods in synchronism with the advance of the first counter through M counts; means coupled to the output of the memory for detecting selected ones of the characters; and means normally rendered effective upon the detection of one of the selected characters for blanking the display during the next clock period.

Claim 12

Apparatus as defined in claim 9, further comprising means renDered effective upon the generation of the cursor control indication for inhibiting the operation of the blanking means during the next clock period.

Claim 13

Apparatus as defined in claim 9, further comprising means rendered effective upon the detection of one of the selected characters for stopping the scanning means during the blanking of the display.