Patent GB-987442-A (GB)
Title: Data transfer system
IPC: H03K5/135
Filed: 1961-11-24
Abstract: 987,442. Electric selective signalling. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 24, 1961 [Dec. 12, 1960], No. 42109/61. Heading G4H. Data pulses issuing from a keyboard on which is entered sales information (date, quantity, type of goods) are sampled by pulses of such frequency that at least one falls completely within a data pulse and an information pulse is transmitted to a utilization device in response to the first sample pulse which falls completely within a data pulse. The significance of numerical items transmitted by depressing keys on a keyboard 104 is indicated by previously pressing a categorizing button on a console 103, such as date button DT, quantity button Q and so on. Before any data is entered a "data ready" button DR is pressed. Each of the keys of the keyboard 104 is sampled in turn and the value of a depressed key is indicated by data pulses in a seven-bit code on parallel lines. While a data pulse is on any of the lines conductor 115 is up and 116 down. While a sample pulse exists line 113 is up and 114 down. The and circuits A 1  to A 5  in response to coincidence of positive inputs produce a negative output. Or circuits -O 1 , -O 2 , in response to a negative input produce a positive output. Operation of keyboard. The "data ready" button DR is first depressed, followed by a category button, say "date" DT, and the keys of number keyboard 104. The "terminate category" button TC is then pressed. The DR and the next required category button is then depressed, the appropriate number entered and the TC button operated. When all items have been entered, the "terminate entry" (TE) button is operated. If sampling shows that the DR button has been depressed the category buttons are sampled to find which has been operated. The keys of keyboard 104 operate sequentially and pass a long pulse MK on to appropriate lines as data pulses. When pulse MK is passed by button TC the category buttons are a gain scanned, or if button TE passes MK the operation stops. Gating data pulses: The first complete sample pulse falling within a data pulse opens gates 110. In such a case line 115 is already up and -O 2  giving a negative output which is inverted at I 2  to send positive one input to and circuit A 2 . When line 113 goes up all inputs to A 2  are positive and a negative output results. This is inverted by I 1  to open gates 110, and also sets the latch comprised of and A 1  and or -O 1 . When line 113 goes down the latch remains set and line 114 goes up operating and A 5 . The resultant positive output of or circuit -O 2  is inverted by I 2  to prevent and A 2  from passing any later sample pulses while the same data pulse is present. When the next sample pulse arrives A 4  operates and maintains the low output of I 2 . This situation is only changed when line 115 goes down, indicating the end of the data pulse, and causes the latch A 1 ,-O 1  to be unset. If a sample pulse arrives when there is no data pulse and A 3  operates and I 2  produces a low output to disenable and A 2 . Then, a data pulse starting while line 113 is still up has no effect on the circuits.