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Circuit Connecting a Calculator to a Microprocessor

IP.com Disclosure Number: IPCOM000087987D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Suding, R: AUTHOR

Abstract

Arithmetic functions may be performed by passing problems from a microprocessor to a calculator for solution. This approach reduces microprocessor memory space and program complexity, as well as saving time.

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Circuit Connecting a Calculator to a Microprocessor

Arithmetic functions may be performed by passing problems from a microprocessor to a calculator for solution. This approach reduces microprocessor memory space and program complexity, as well as saving time.

Normally, the calculator (for example, a MOS Technology 2529-103) performs arithmetic functions specified at inputs Y1-Y4 upon data supplied serially by digits at the same inputs. Display segment outputs appear serially by digit at segment outputs A, B, E, F, G and DP. Twelve display digits are handled in sequence by serially scanning the digits with signals on twelve digit lines.

Here, the serially activated twelve digit lines are connected to the line inputs of a decoder/selector (such as a 74150) and four bits 0-3 from a microprocessor are connected to its select inputs. When the one, of the twelve, line inputs designated at the select inputs is scanned internally by the calculator, a signal appears at the decoder/ selector output. A register (such as a 7442) stores digit signals on three additional microprocessor inputs 4-6 at the time that the decoder/ selector output occurs. These stored digits are entered as data and functions into the calculator inputs.

An additional microprocessor input 7 specifies when the microprocessor is ready to receive the calculated result. When a signal appears on the calculator digit line identified by the microprocessor, a data-ready pulse interrupts the microprocessor, wh...