Claims
- 1. In an erasing typewriter including
- key actuated means for generating signals representing an actuated key,
- memory means for storing an ordered sequence of signals representing a sequence of operator actuated keys,
- print means including print and erase media for executing a print cycle to at times print a character at a print point if said print medium is enabled, or to erase a character at a print point if said erase medium is enabled,
- print point position control means responsive to said key actuated means for displacing said print means and for accessing a selected location of said memory means corresponding to said print point, and
- erase means operative in response to actuation of an erase key for initiating a sequence of operations including:
- (a) actuating said print point position control means to displace said print point one character space toward a left margin,
- (b) accessing said memory means at a selected location corresponding to said displaced print point for reading signals stored at said selected location,
- (c) actuating said print means and enabling said
- erase medium to execute a print cycle to erase a character at said print point corresponding to signals read from said memory means,
- the improvement comprising:
- first means responsive to absence of signals representing an erasable character at said selected location of said memory means to inhibit said print cycle and to enable said erase medium and said print means to execute a print cycle on a following key actuation only if said following key actuation corresponds to actuation of a key representing an erasable character.
- 2. The apparatus of claim 1 in which said first means includes
- latch means set to a distinctive condition only when said erase key is actuated and said selected location of said memory means does not contain an erasable character.
- 3. The apparatus of claim 2 which includes input means to set said latch means if said memory means contains signals representing a typewriter function or is empty at said selected location.
- 4. The apparatus of claims 2 or 3 which includes
- logic means distinctively operated in response to depression of a printable character key when said latch means is set to execute an erase function and to reset said latch means.
- 5. The apparatus of claims 2 or 3 which includes
- logic means distinctively operated if a typewriter function key is depressed when said latch means is set to execute a corresponding function and to reset said latch means.
- 6. The apparatus of claims 2 or 3 which includes
- logic means distinctively operated if a typewriter space bar is depressed when said latch means is set to execute a no print, no escape cycle and to reset said latch means.
- 7. The apparatus of claim 2 or 3 which includes
- logic means distinctively operated if said erase key is depressed when said latch means is set to initiate an automatic erase cycle and to reset said latch means.
CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS
This is a continuation-in-part of co-pending application Ser. No. 116,733 filed Jan. 30, 1980, now abandoned in favor of this application. Reference is made to U.S. Pat. Nos. 3,724,633 and 3,780,846, and to copending Bowles et al applications Ser. No. 908,315 (LE977-014) entitled "Erase Through Tab" now U.S. Pat. No. 4,245,918, and Ser. No. 908,314, (LE977-016) entitled "Underscore Erase" now abandoned in favor of application Ser. No. 227,878, filed Jan. 23, 1981. The first mentioned patent discloses a typewriter with the capability of effectively erasing an individual character. The second mentioned patent discloses an automatic erasing typewriter in which the character which is erased is determined by signals stored in a line memory. The two referenced applications disclose improvements allowing the erase function to proceed through a tab, and to erase the underscore graphic of an underscored character.
US Referenced Citations (5)
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
116733 |
Jan 1980 |
|