Synchronization system for key telephone system

• US 4,583,221 A
• Filed: 10/26/1983
• Issued: 04/15/1986
• Est. Priority Date: 10/27/1982
• Status: Expired due to Fees

• Current Assignee: Iwasaki Tsushinki Kabushiki Kaisha (Iwatsu Electric Company Limited)
• Original Assignee: Iwasaki Tsushinki Kabushiki Kaisha (Iwatsu Electric Company Limited)
• Inventors: Uchida, Seiya, Ono, Takao
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Chin, Wellington
• Application Number:
  US06/545,539
• Time in Patent Office: 902 Days
• Field of Search: 370/29, 370/100, 375/114, 375/117, 179/90 K
• US Class Current: 370/509
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04L 7/044 using a single bit, e.g. start stop bit
• CPC Class Codes: H04L 7/10 Arrangements for initial synchronisation
• CPC Class Codes: H04M 9/003 Transmission of control signals from or to the key telephone set; signalling equipment at key telephone set, e.g. keyboard or display equipment keyboard equipment in semi-automatic systems H04M3/62

Abstract

A synchronization system for a key telephone system, in which information signals are transmitted in a time-division manner between a key service unit and each key telephone set. The information signal is formed by a control signal, a first signal transmitted from the key service unit to the key telephone set and a second signal from the key telephone set to the key service unit. The control signal is formed by a start signal of one-pulse and a variable synchronizing code, which is placed in a time slot following the start signal and which is formed by a plurality of pulses assuming one of predetermined consecutive values in a predetermined order for each transmission frame period. The control signal is transmitted from the key service unit to each key telephone set for each frame period in synchronism with a first counter provided at the key service unit for developing standard of transmission timings. At the key telephone set, the detecting position of the variable synchronizing code in a next frame period performed under control of controlled standard timings, which are developed by a second counter provided at the key telephone set, is shifted by one pulse until a correct start signal is detected if the variable code is not correctly detected in a certain frame period. As a result of the above operations, the standard transmission timings and the controlled transmission timings are synchronized with each other.

Claims

1. A synchronization system for a key telephone system in which information signals are transmitted in a time-division manner between a key service unit and each key telephone set,

characterized in that the information signal is composed of a control signal of one-pulse start signal and a variable synchronizing code, which is placed in a time slot following the start signal and which is formed by a plurality of pulses assuming one of predetermined consecutive values in a predetermined order for each transmission frame period, a first signal to be transmitted from the key service unit to the key telephone set and a second signal to be transmitted from the key telephone set to the key service unit, the signal format of the information for each period being formed so that the control signal is followed by the first signal and the second signal allocated in a predetermined order;

that the key service unit is provided with a first counter employed for developing standard transmission timing, a first signal generator for generating the start signal and a second signal generator for generating the variable synchronizing code; and

that each key telephone set is provided with a second counter for developing controlled transmission timing, a first detector for detecting the start signal under control of the controlled transmission timing, a second detector for detecting the variable synchronizing code under control of the controlled transmission timing, and control means for repeating operations of shifting by one pulse the detecting position of the variable synchronizing code by said second detector in a next period until a correct start signal and a correct synchronzing code are detected by said first detector and said second detector in combination if the variable synchronizing code is not correctly detected by said second detector in a certain frame period, whereby said first counter and said second counter are synchronized with each other,

said second detector comprising a shift register for temporarily storing the variable synchronizing code of each frame period, an adder for adding by "1" to the contents of said shift register to produce an added output, a standby register for temporarily storing the added output until the added output is refreshed at the next frame period, and a comparator for comparing the contents of said shift register and the contents of said standby register when the variable synchronizing code is newly stored in said shift register in each of the periods to provide a coincident output as a correct detection output of the variable synchronizing code.

2. A synchronization system for a key telephone system in which information signals are transmitted in a time-division manner between a key service unit and each key telephone set,

characterized in that the information signal is composed of a control signal of one-pulse start signal and a variable synchronizing code, which is placed in a time slot following the start signal and which is formed by a plurality of pulses assuming one of predetermined consecutive values in a predetermined order for each transmission frame period, a first signal to be transmitted from the key service unit to the key telephone set and a second signal to be transmitted from the key telephone set to the key service unit, the signal format of the information for each period being formed so that the control signal is followed by the first signal and the second signal allocated in a predetermined order;

that the key service unit is provided with a first counter employed for developing standard transmission timing, a first signal generator for generating the start signal and a second signal generator for generating the variable synchronizing code; and

that each key telephone set is provided with a second counter for developing controlled transmission timing, a first detector for detecting the start signal under control of the controlled transmission timing, a second detector for detecting the variable synchronizing code under control of the controlled transmission timing, and control means for repeating operations of shifting by one pulse the detecting position of the variable synchronizing code by said second detector in a next period until a correct start signal and a correct synchronizing code are detected by said first detector and said second detector in combinatin if the variable synchronizing code is not correctly detected by said second detector in a certain frame period, whereby said first counter and said second counter are synchronized with each other,

said control means comprises a scale of (N-n) counter, where N is the number of pulses in each frame period and n is the number of pulses of the variable synchronizing code, to produce an output assuming a true state when counting its input pulses until a carry pulse is obtained from the scale of (N-n) counter so that the counting operation of said second counter is temporarily stopped by the true state of the output on the scale of (N-n) counter, and a gate for passing the input pulses of the scale of (N-n) counter only a duration from a time when the variable synchronizing code is not correctly detected by said second detector to a time when the scale of (N-n) counter generates the carry pulse.