Browse Prior Art Database

Electronic Tab/Backspace Control

IP.com Disclosure Number: IPCOM000074221D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Fulbright, NE: AUTHOR [+3]

Abstract

The object of this feature is to provide an electronic means for controlling tabulating functions for a remotely controlled serial printer. This allows the replacing of mechanical tab stops with a form of inexpensive electronics which makes remote tab operations economical to implement in a controlled terminal.

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Electronic Tab/Backspace Control

The object of this feature is to provide an electronic means for controlling tabulating functions for a remotely controlled serial printer. This allows the replacing of mechanical tab stops with a form of inexpensive electronics which makes remote tab operations economical to implement in a controlled terminal.

The method outlined uses two shift registers shifted by a common clock source 1 so that they always shift together. The registers are made up of MOSFET type shift registers 2 and 3 with the addition to each shift register 2 and 3 of two discrete register positions 4, 5 and 6, 7 that have the capability of being set and reset by the control logic. This combination affords the economy of the MOSFET registers for the bulk of the hardware but provides the flexibility necessary through the use of the discrete elements.

The total number of positions in each register 2, 4, 5, or 3, 6, 7 is determined by the number of print positions on the printer. The tab register 2 is used to store indicators to represent the tab stops. Each time the print mechanism in a terminal moves one position, both shift registers are advanced one position. When a tab position is to be set, a bit is stored in the tab register 2, 4, 5 at the desired location.

The locate register 3, 6, 7 is primarily concerned with maintaining the proper relationship between the shift registers and the printer mechanics in the terminal. A left margin bit stored in the locate register 3, 6, 7 is brought to the "initial" position each time a carriage return is performed at the printer. Since the tab 2 and locate registers 3 shift together, the tab stop bits stored in the tab register 2 always maintain their respective locations with reference to the left margin bit in register 3.

The following are brief descriptions of the operations performed by the tab/backspace logic. T:ABFORWARD:.

The tab position indicator bits are stored in the tab shift register 2, 4, 5 by tab set circuits 11 and by tab reset circuits 12. During a tab operation latch 8 is set and the tab register is shifted for each printer space movement until a tab bit is detected in the first discrete register position 4. This, with the set latch 8, generates a stop signal through AND 9 to line 10 to the printer mechanics to start a mechanical "slowdown". The inertia of the mechanics causes one more space shift which is detected when the bit shifts to the second discrete register position
5. The presence of this bit in position 5 indicates the end of the tab operation and that the mechanics are fully stopped. CARRIAGE RETURN:.

During an initial power on reset in...