ARRANGEMENT AND METHOD AT AN INTEGRATED CIRCUIT

Abstract: The present invention concerns an arrangement and process for mutually synchronizing application-specific integrated circuits (ASIC) which are arranged to communicate with one another. The arrangement according to the invention enables an activating pulse edge to be determined in a common clock signal to an edge-triggered integrated circuit which communicates with at least one further integrated circuit. Each of the communicating integrated circuits receives the common clock signal. The circuits also receive frequency data in the form of a clock signal which is adapted to the respective circuit and which is used for determining in the respective circuit the activating pulse edge in the common clock signal.

Description: Arrangement and method at an integrated circuit The present invention concerns a process and arrangement for the mutual synchronization of application-specific integrated circuits (ASIC) arranged to communicate with one another. TECHNICAL BACKGROUND In the field of telecommunications, inter alia, digital systems are found which consist of several different application-specific integrated circuits which often cooperate in such a way that data has to be transmitted between the different circuits. Each operation or change of state in an integrated circuit is initiated by a clock signal which can be generated in the circuit or can be input into the circuit from a clock disposed externally thereof. It is important that the parts of an integrated circuit which are interdependent or communicate with one another in some way are synchronized in terms of time. This synchronization is brought about by the clock signal which has to be distributed such that clock skew between clock signals in the different parts of the integrated circuit is nTjxumized. In the case of a digital system comprising a plurality of application-specific integrated circuits (ASIC), all the changes of state or operations in the system are controlled by clock signals which correspond to the circuits and are usually generated locally in connection with the respective circuit. In the same way as for different parts of an integrated circuit, it is important that different integrated circuits in a digital system are synchronized in terms of time if these circuits are arranged to exchange data. In the case of a system with a plurality of integrated circuits cooperating with one another there should therefore be correspondance between clock signals belonging to respective circuits. If this is not the case, clock skew can occur between clock signals in the different circuits in the system, which leads to problems when data is exchanged therebetween. L'S-A-5 317 601 earlier disclosed a technique for feeding clock signals at different frequencies to a number of different pans of an integrated circuit. Λ number of clock sienals are ceneraicd and distributed to the different parts of the circuit. In order to improve control of clock skew between these synchronized clock signals a synchronizing signal is also generated and is used as a reference for the clock signal. This synchronizing signal is distributed to the different parts of the integrated circuit. A synchronizing circuit adapted to each part of the integrated circuit receives the clock signals and the synchronizing signal. The synchronizing circuit essentially comprises a multiplexer which through-connects the clock signal to the intended part of the integrated circuit under the control of the synchronizing signal. Each synchronizing circuit therefore synchronizes the respective clock signal according to the synchronizing signal. The known synchronizing circuit consequently overcomes the problem of reducing skew between synchronizing signals to different parts of an integrated circuit. However the solution can be inadequate when data is exchanged between these parts. DESCRIPTION OF THE INNENΗON The object of the present invention is to solve the problem of improving synchronization between integrated circuits which communicate with one another. This object is achieved for respective integrated circuits by means of an arrangement and a process whereby an activating pulse edge in a common clock signal to an edge-triggered integrated circuit can be deterrnined. The integrated circuit is arranged to communicate with at least one further integrated circuit. Each of the circuits, which are arranged to communicate with one another, receives the common clock signal. The different integrated circuits are also arranged to receive frequency data in the form of a clock signal which is adapted to the respective circuit and which is used for establishing in the respective integrated circuit an activating pulse edge in the common clock signal. The arrangement according to the invention comprises a switching device and an edge-triggered storage member. The switching device is arranged to receive a clock signal which is adapted to the integrated circuit and which has a lower frequenc\ than the common clock siεnal. The storage member is in turn arranoed to receive an output signal from the switching device which can change between a first and a second state depending on the clock signal adapted to the integrated circuit. In the first state of the switching device an input signal from a second integrated circuit with which the integrated circuit communicates is through-connected. In the second state of the switching device an output signal from the storage member is fed back through the switching device and back to the same storage member. DESCRIPTION OF THE FIGURES Figure 1 shows three application-specific integrated circuits with separate clock signals; Figure 2 shows three application-specific integrated circuits which receive a common clock signal; Figure 3 shows some examples of clock signals; and Figure 4 shows the arrangement according to the invention. PREFERRED EMBODIMENT In the following the invention will be explained in greater detail with reference to the Figures and in particular Figures 2 and 4, Figure 2 showing a digital system in the case of which a common clock signal CLK is coupled into a plurality of application- specific integrated circuits ASIC1, ASIC2, ASIC3, and Figure 4 showing an arrangement in the case of which an activating pulse edge in the common clock signal CLK can be determined for the respective integrated circuit. Figure 1 shows a system according to the prior art. The system comprises means 1 for generating a common clock frequency. As the Figure shows, the clock frequencies φl. φ2. φ3 adapted to the respective circuit can be generated from the common clock signal CLK by means of a frequency divider 2. Each of the application-specific integrated circuits ASIC1. ASIC2. ASIC3 shown in the Figures receives the clock signal φl . φ2. φ3 adapted to the respective circuit. However with the solution shown problems arise when data has to be exchanged between the integrated circuits ASIC1. ASIC2. ASIC3. As a result of delays in the frequenc> divider 2. for example, differences in s>τιchronization can occur between the clock signals φl . φ2. φ3 in the respective integrated circuits, i.e. problems with clock skew occur when data is exchanged between the circuits. The arrangement according to the invention is intended for clock pulse distribution according to Figure 2. A common clock signal CLK is generated and transmitted to a frequency divider 2 which generates three new clock signals φl, φ2, φ3 from the common clock signal CLK. These three new clock signals are adapted to the requirement in the respective application-specific integrated circuit ASICl, ASIC2. ASIC3. However each of the application-specific integrated circuits also receives the common clock signal CLK which is transmitted with a nώiimum relative delay to each of the integrated circuits. Each integrated circuit ASICl, ASIC2, ASIC3 thus receives two different clock signals at different frequencies. The integrated circuits are arranged to communicate with one other, which is shown in the Figures by the connection from each of the circuits to a common databus 3. Figure 3 shows an example of a common clock signal CLK, a first clock signal φl which is adapted to a first integrated circuit ASICl and a second clock signal φ2 which is adapted to a second integrated circuit ASIC2. The first and second clock signals φl, φ2 are generated from the common clock signal CLK. The Figure shows the situation at the input of the first integrated circuit ASICl and at the input of the second integrated circuit ASIC2. As the Figure clearly shows, a given delay has occurred in the first clock signal φl and in the second clock signal φ2 in relation to the common clock signal CLK. Both the first and the second clock signals are consequently phase-shifted relative to the common clock signal CLK. A given delay has also occurred between the first clock signal φl and the second clock signal φ2. even though this delay is considerably shorter in the case shown. In spite of the fact that the delay is relatively short, this clock ske can give rise to problems when the first and second integrated circuits communicate with each other. It is therefore advantageous to attempt to reduce the clock skew between the clock signals φl . φ2 in these two circuits whenever data is exchan g ed. Figure 4 shows the arrangement according to the invention. 1 iis arrangement enables the s\nchronization of each application-specific integrated circuit ASICl . ASIC2. ΛS1C3 to be adapted to the common clock signal CLK. Each input of data into a first integrated circuit ASICl is thereby performed synchronously with the common clock signal CLK in spite of the fact that the circuit is controlled by a first clock signal φl which has a first clock frequency. A switching device 5 receives the first clock signal φl and is actuated thereby such that it changes between a first and a second state. This change occurs for each edge of a clock pulse in the first clock signal φl adapted to the circuit such that the switching device 5 is in the first state for the entire clock pulse, i.e. the period of time between a positive edge and a negative edge following the latter in the first clock signal φl . In the first state of the switching device 5 new data is input at the input of the arrangement 4. This means that an input signal IN to the arrangement 4 is coupled unaffected through the switching device. The input signal IN shown in the Figure corresponds to a signal from for example the second integrated circuit which is controlled by the second clock signal φ2. A storage member 6 is arranged for the intermediate storage of the input signal IN. The changes of state of the storage member 6 are controlled by the common clock signal CLK which means that input into and output from the storage member 6 occurs at a higher frequency than the input into the switching device 5. The storage member 6 receives the output signal from the switching device 5 during a first clock pulse and this signal can already be received at the output of the storage member 6 during the same clock pulse. The storage member is arranged to store the input signal until a new input occurs during a subsequent clock pulse. Consequently intermediate storage occurs during a clock cycle in the common clock signal CLK. During an intermediate period before a ne clock pulse is received in the first clock signal φl it is important that the output signal OUT from the arrangement 4 to the first integrated circuit ASICl remains constant. The integrated circuit ASICl triggers on the positive edge of a clock pulse in known manner in the first clock signal φl and the output signal OUT of the arrangernent should therefore not be changed before a new clock pulse is received in the first clock signal φl . In order to enable an unchanged output signal to be output during a plurality of clock cycles in the common clock signal, the output signal from the storage member 6 is fed back to the switching device 5. When the switching device 5 changes to the second state, the fed-back output signal is through-connected to the storage member 6 which, during the subsequent clock pulse in the common clock signal CLK, through-connects the same signal to the storage member output, which signal constitutes the output signal from the arrangement. When a new clock pulse is received in the first clock signal, the switching device returns to the first state again and an input signal to the circuit can be fed through the switching device to the storage member. This input signal can then be fed further, by further synchronization, to the integrated circuit from the storage member. For the second integrated circuit ASIC2 shown in Figure 2 the frequency for the second clock signal φ2 is precisely one quarter of the frequency for the common clock signal CLK, The use of the arrangement 4 according to the invention in the second integrated circuit ASIC2 thus means that data from some other integrated circuit ASICl, ASIC3 can be coupled through the switching device 5 during the first clock pulse in the second clock signal φ2. The output signal OUT from the arrangement 4, i.e. from the storage member 6, responds to the input signal IN as quickly as the next positive edge is detected in the common clock signal CLK. By means of this clock pulse in the second clock signal φ2 an activating pulse edge is therefore selected in the common clock signal CLK. During the following three clock pulses of the common clock signal CLK the output signal from the storage member 6 is fed back through the switching device, which means that the output signal OUT from the arrangement 4 remains unchanged during these pulses. The output signal OUT therefore remains unchanged during the total four clock pulses from the common clock signal CLK. A ne input signal IN is input into the switching dev ice 5 when a clock pulse is again received from the other clock signal φ2. This new input signal IN is processed as indicated above. The arrangement according to the invention and shown in Figure 4 is arranged for connection to an input on each of the integrated circuits ASICl. ASIC2. ASIC3 which are arranged to communicate with one other. By means of the arrangement 4 according to the invention a clock signal adapted to the circuit is synchronized with a clock signal CLK which is common to all the communicating integrated circuits ASICl, ASIC2, ASIC3. The output signal OUT from the arrangement 4 according to the invention constitutes the input signal to the corresponding integrated circuit.

Claims: CLAIMS 1. Arrangement for determining a first activating pulse edge in a common clock signal (CLK) at a frequency to a first edge-triggered integrated circuit (ASICl) which is arranged to communicate with at least one further edge-triggered integrated circuit (ASIC2; ASIC3) with a second activating pulse edge in the common clock signal (CLK), characterized in that - a switching device (5) is arranged to receive frequency data in the form of a first clock signal (φl) which is adapted to the first integrated circuit (ASICl) and has a lower frequency than the frequency of the common clock signal (CLK); - a storage member (6), which is edge-triggered by the common clock signal (CLK), is arranged to receive an output signal from the switching device (5) and to provide an output signal (OUT) from the arrangement (4); and in that - the switching device (5) is arranged to change between a first state and a second state dependent on the first clock signal (φl), in which first state an input signal (IN) from the second integrated circuit (ASIC2; ASIC3) is through-connected to the storage member (6) and in which second state an output signal from the storage member (6) is fed back to the same storage member (6). 2. Arrangement according to Claim 1. characterized in that the storage member (6) is arranged to trigger on a positive edge of a clock pulse in the common clock signal (CLK). 3. Arrangement according to Claim 1 or 2. characterized in that the switching device (5) is arranged to change state in the case both of positive and negative edges of a clock pulse in the first clock signal (φl ). 4. Process for determining a first activating pulse edge in a common clock signal (CLK) at a frequency to a first edge-triggered integrated circuit (ASICl ). an input signal (IN) being received from at least one second edge- triggered integrated circuit (ASIC2: ASIC3) with at least one further activating pulse edge in the common clock signal (CLK). characterized in that: - frequency data in the form of a first clock signal (φl ) which is adapted to the first integrated circuit (ASICl) and has a lower frequency than the frequency for the common clock signal (CLK) is received in the switching device (5); - the input signal (IN) is received in the switching device (5); - an output signal from the switching device (5) is received in a storage member (6) edge-triggered by the common clock signal; - the switching device (5) is actuated such that it changes between a first and a second state dependent on the first clock signal (φl); - the input signal is connected through the switching device (5) in the first state; - an output signal from the storage member (6) is fed back through the switching device (5) to the same storage member (6) in the second state; and in that - the output signal from the storage member (6) constitutes the output signal (OUT) from the arrangement (4).

Inventors: HINTUKAINEN KARI, HINTUKAINEN, KARI
Applicants: ERICSSON TELEFON AB L M, HINTUKAINEN KARI, HINTUKAINEN, KARI, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 1996
Main classification: G06F1
IPC codes: G06F1, H03K5