System bus control system

Abstract: A system bus control system for controlling the data transmission between a master system and a plurality of slave systems coupled to the master system through system buses, wherein the master system sends to the slave systems first strobe signals representing the data transferring timing and second strobe signals delayed by a predetermined period of time which corresponds to the accessing time, on the other hand, the slave systems output replying signal to the master system when the slave systems receive the first strobe signal and in turn receiving the second strobe signal, the slave system sends the replying signal to the master system.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a combination of a system bus with a master system and slave systems including a system bus control system used for controlling data transmission between the master system and the slave systems connected by said system bus and to a method of controlling data transmission in a system having said combination. Description of the Prior Art Conventionally, as a system bus control system of the above type, there has been known such a system that a master system sends a series of data transferring strobe signals for designating the data transferring timing corresponding to respective slave systems. Upon receipt of the data transferring strobe signal corresponding to the slave systems respectively, the slave system which has received the corresponding strobe signal starts count an accessing time, and after the accessing time has been counted, a data transferring replying signal is outputted from the slave system to the master system. Figs. 1 and 2 show the read timing and write timing of the multi bus employed in the conventional system bus control system mentioned above. Figs. 3 and 4 show the timing in a one-Byte read cycle and the timing in a one-Byte write cycle at the VME bus employed in the conventional system bus control system. The data transferring strobe signals are shown by MRDC* and IORC* in Fig. 1, MWTC* and IOWC* in Fig. 2 and DS0* and DS1* in Figs. 3 and 4. The data transferring and replying signals are shown by XACK* in Figs, 1 and 2, DTACK* and BERR* in Figs. 3 and 4. In Figs. 3 and 4, IACK*shows interrupt acknowledge signal, A01 to A31, AM0 to AM5 and LWORD* show address data, AS* shows an address strobe signal representing the decision of the address, WRITE* shows read/write signal and D00 to D07 show the transferring data. When the master system outputs the data transferring strobe signal to the slave systems and the corresponding data transferring strobe signal is received by the slave system, which outputs the data transfer and replying signal to the master system after the data accessing time has been counted. Fig. 5 shows an example of a conventional circuit arrangement of a data transferring and replying signal unit used in the slave system of the access time of 200 nano seconds.. The data transferring and replying signal unit comprises a 10MHz clock generator 111, a shift register 113 having three flip-flops 112, an OR gate 114, an AND gate 115, a tri-state output gate 116 and a decode circuit 117. In the circuit arrangement mentioned above, when the data transferring strobe signal MRDC* or IORC* sown in Fig. 1 becomes active, or the data transferring strobe signal MWTC* or IOWC* in fig. 2 becomes active, the time counting is started, and after the time corresponding to the accessing time has been counted, the data transferring and replying signal XACK* is outputted. In the conventional system bus control system, it is necessary to provide a circuit arrangement including a set of shift registers or a counter for counting the accessing time, therefore, there is such a problem that the circuit arrangement of the slave system is much complicated. SUMMARY OF THE INVENTION An essential object of the present invention is to provide a system bus control system and a system bus control method in which the slave system does not require to provide any shift register or counter for counting the accessing time. The above object is solved, according to the invention by a combination of a system bus connected with a master system and slave systems and including a system bus control system for controlling data transmission between said master system and a plurality of said slave systems through said system bus, wherein said master system during a read and write cycle respectively outputs on said system bus address signals to read and write data from and to the slave systems and comprises a strobe signal generator for outputting on said system bus to said slave systems during the time of outputting a given address signal: (1) a first strobe signal, the commencement of which is delayed so that it starts after said given address signal is stabilized, and (2) a number of subsequent, sequential strobe signals, which are each commenced one by one with a predetermined time interval, said master system further comprising means for outputting during a write cycle data to be written to the addressed slave system; each slave system which has an access time which may vary from the access time of the other slave systems includes a data transferring and replying unit for receiving said address signal and said first strobe signal and at least one of said sequential, subsequent strobe signals from said system bus, and each of said slave systems during a write and read cycle of the master system is respectively reading data from and outputting data to said system bus such that, in response to an address signal which addresses a particular slave system and in response to said first strobe signal said addressed slave system outputs data to said system bus in a read cycle of said master system and said data transferring and replying unit of the addressed slave system, when it receives at least one of said subsequent, sequential strobe signals sends to said master system an answering signal which causes: said master system to read in said read cycle from said system bus said data as output by said addressed slave system, said strobe signal generator of said master system to temporarily terminate sending said first and all of said subsequent, sequential strobe signals, and said master system to terminate the address signal until said addressed slave system stops outputting its data to the system bus and its data transferring and replying unit renders the answering signal non-active in response to said termination of one of the first and subsequent, sequential strobe signals from the strobe signal generator of the master system, and wherein said master system further writes in its write cycle the data which it has already put out to the system bus in the addressed slave system at a time after the answering signal is turned to active (claim 1). The above object is further solved by a method for controlling data transmission in a system in which a system bus is combined and connected with a master system and a plurality of slave systems, wherein (a) said master system has a read and a write cycle for respectively reading and writing data and outputting to said system bus: i) an address signal, ii) a first strobe signal, the commencement of which is delayed so that it starts after said given address signal is stabilized, and iii) a number of subsequent sequential strobe signals, which are each commenced one by one with a predetermined time interval, and iv) during a write cycle data to be written to the addressed slave system, and (b) each slave system has an access time which may vary from the access time of the other slave systems and is adapted to receive said address signal, said first strobe signal and at least one of the subsequent sequential strobe signals from said system bus and, during a write and read cycle of the master system, is respectively reading data from and outputting data to said system bus such that, in response to an address signal which addresses a particular slave system and in response to said first strobe signal said addressed slave system writes data to said system bus in a read cycle of said master system and, when said addressed slave system receives at least one of said subsequent sequential strobe signals, sends to said master system an answering signal which causes the master system to read in its read cycle from said system bus the data as output by said addressed slave system and to temporarily terminate sending said first and all of said subsequent, sequential strobe signals and to terminate the address signal until said addressed slave system stops outputting its data to the system bus and renders the answering signal non-active in response to said termination of one of said first and subsequent sequential strobe signals from the master system, and wherein said master system further writes in its write cycle the data which it has already put out to the system bus in the addressed slave system at a time after the answering signal is turned to active (claim 4). Preferably, said number of subsequent, sequential strobe signals is determined such that the last of it is delayed from said first strobe signal by a time-period in excess of the slowest access time of said plurality of slave systems. Further, each of said plurality of slave systems includes an address decoder for determining whether the data from said system bus is addressed to said respective slave system. In operation, the master system sends to the respective slave system the first strobe signal representing the data transferring timing and the of subsequent, sequential strobe signals, each being delayed from the first strobe signal by a predetermined period of time which corresponds to the access time. The addressed slave system outputs the answering signal to the master system when the addressed slave system receives one of said of subsequent, sequential strobe signals after receipt of the first strobe signal and sends the answering signal via the system bus to the master system. Therefore, there is no need to provide any counter or shift registers in the slave system for counting the access time. BRIEF EXPLANATION OF THE DRAWINGS Fig. 1 is a time chart for showing the write timing in the multi bus of the conventional system bus control system, Fig. 2 is a time chart for showing the read timing in the multi bus of the conventional system bus control system, Fig. 3 is a time chart for showing the timing in the VME bus in the read cycle in an example of a prior art, Fig. 4 is a time chart for showing the timing in the VME bus in the write cycle in the prior art, Fig. 5 is a circuit diagram of a conventional data transferring and replying unit, Fig. 6 is a time chart for showing the read timing in an embodiment of the system bus control system according to the present invention, Fig. 7 is a time chart for showing the write timing in the embodiment of Fig. 6, Fig. 8 is a circuit diagram of an embodiment of a strobe signal generating circuit for performing the time charts shown in Figs. 6 and 7, Fig. 9 is a state shift chart of the strobe signal in the embodiment of Fig. 8, Fig. 10 is a circuit diagram showing an embodiment of a data transferring and replying unit, Fig. 11 is a time chart for showing the data read timing in the embodiment using the data transferring and replying unit shown in Fig. 10, and Fig. 12 is a block diagram showing relation between the master system and the slave system for an embodiment of the present invention DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 6, the master system sends the address data to an address bus (not shown) and after the address data is stabilized, the master system makes the strobe signal STB1* active. Further the master system makes the respective strobe signals STB2*, STB3*, ... STBn* active sequentially one by one in the written order with a predetermined time period, for example, every 100 nano seconds. The last strobe signal STBn* is activated after such a time period that the access time of the slave system has passed from the activating time of STB1*. When the addressed slave system receives the strobe signal STB1*, the data of the slave system to be read by the master system is put out to the data bus. When the slave system receives the strobe signal STBn*, an answering signal RDY* is activated. Receiving the answering signal RDY*, the master system reads the data on the data bus and makes all of the strobe signals STB1* to STBn* non-active. Thereafter the master system stops outputting the address data. When the signal STB1* becomes non active, the slave system stops outputting the data to the data bus, and the signal "RDY*" is made non-active. In Fig. 7, the master system writes the data which has already been outputted to the data bus by the slave system after the signal RDY* is turned to active. Other operations are the same as shown in Fig. 6. Usually the access time of the slave system such as an I/O device or a memory is less than 300 nano seconds, therefore, if the time difference of the adjacent strobe signals is 100 nano seconds, it is sufficient to provide four strobe signals. Fig. 8 shows a strobe signal generator for generating three strobe signals. The circuit shown in Fig. 8 comprises three OR gates 31, four AND gates 32 and three flip flops 33. With the bus use start signal "start" and clock signals , the respective strobe signals STB1*, STB2* and STB3* are sequentially activated in the order as described. When RDY* is activated, the strobe signals mentioned above are inactivated. Fig. 9 shows state shifts of the circuit shown in Fig. 8. The states of the strobe signals [STB1*, STB2* and STB3*] are [1, 1, 1] when the signal START = 0. When the signal START changes to equal 1, the state changes to [0, 1, 1] (state of STB1* changes to zero). During the time period when START is non-active, that is when RDY* = 1, the subsequent strobe signals change from [0, 0, 1] to [0, 0, 0]. In the course of these state shifts as mentioned above, if the signal RDY* becomes 0, the original state can be restored. Fig. 10 shows a circuit diagram of a data transferring and replying unit of a slave system having an access time of 200 nano seconds and connected to a system bus which is operated with strobe signals having a time difference of 100 nano seconds and Fig. 11 shows its data reading timing. This circuit includes an AND gate 51, a tri-state output gate 52 and a decode circuit 53. When the first strobe signal STB1* becomes active, the output of the tri-state output gate 52 turns to a high impedance condition and outputs the signal "RDY*" of non-active. Upon receipt of the signal "STB3*", the signal "RDY*" is made active. As shown in Fig. 10, the circuit arrangement of the data transferring and replying unit becomes remarkably simple compared to the conventional data transferring and replying unit as shown in Fig. 5. As described above, according to the system bus control system of the present invention, since it is unnecessary to provide any shift register or counter for counting the accessing time in the slave system, the configuration of the slave system can be simplified.

Claims: A combination of a system bus connected with a master system and slave systems and including a system bus control system for controlling data transmission between said master system and a plurality of said slave systems through said system bus, wherein said master system during a read and write cycle respectively outputs on said system bus address signals to read and write data from and to the slave systems and comprises a strobe signal generator (Fig. 8, 31-33) for outputting on said system bus to said slave systems during the time of outputting a given address signal: (1) a first strobe signal (STB1*), the commencement of which is delayed so that it starts after said given address signal is stabilized, and (2) a number of subsequent, sequential strobe signals (STB2*...STBn*), which are each commenced one by one with a predetermined time interval, said master system further comprising means for outputting during a write cycle data to be written to the addressed slave system; each slave system which has an access time which may vary from the access time of the other slave systems includes a data transferring and replying unit (Fig. 10, 51-53) for receiving said address signal and said first strobe signal (STB1*) and at least one of said sequential, subsequent strobe signals (STB2*...STBn*) from said system bus, and each of said slave systems during a write and read cycle of the master system is respectively reading data from and outputting data to said system bus such that, in response to an address signal which addresses a particular slave system and in response to said first strobe signal (STB1*) said addressed slave system outputs data to said system bus in a read cycle of said master system and said data transferring and replying unit of the addressed slave system, when it receives at least one of said subsequent, sequential strobe signals (STB2*...STBn*) sends to said master system an answering signal (RDY*) which causes: said master system to read in said read cycle from said system bus said data as output by said addressed slave system, said strobe signal generator of said master system to temporarily terminate sending said first and all of said subsequent, sequential strobe signals (STB2*...STBn*), and said master system to terminate the address signal until said addressed slave system stops outputting its data to the system bus and its data transferring and replying unit renders the answering signal (RDY*) non-active in response to said termination of one of the first and subsequent, sequential strobe signals from the strobe signal generator of the master system, and wherein said master system further writes in its write cycle the data which it has already put out to the system bus in the addressed slave system at a time after the answering signal (RDY*) is turned to active. The combination of claim 1, wherein said number of subsequent sequential strobe signals (STB2* ... STBn*),generated by said strobe signal generator is such that the last of it (STBn*) is delayed from said first strobe signal (STB1*) by a time period in excess of the slowest access time of said plurality of slave systems. The combination of claim 1, wherein said data transferring and replying unit of each of said plurality of slave systems includes an address decoder (53) for determining whether the data from said system bus is addressed to the respective slave system. A method for controlling data transmission in a system in which a system bus is combined and connected with a master system and a plurality of slave systems, wherein (a) said master system has a read and a write cycle for respectively reading and writing data and outputting to said system bus: i) an address signal, ii) a first strobe signal (STB1*), the commencement of which is delayed so that it starts after said given address signal is stabilized, and iii) a number of subsequent sequential strobe signals (STB2*...STBn*),which are each commenced one by one with a predetermined time interval, and iv) during a write cycle data to be written to the addressed slave system, and (b) each slave system has an access time which may vary from the access time of the other slave systems and is adapted to receive said address signal, said first strobe signal (STB1*) and at least one of the subsequent sequential strobe signals (STB2*...STBn*) from said system bus and, during a write and read cycle of the master system, is respectively reading data from and outputting data to said system bus such that, in response to an address signal which addresses a particular slave system and in response to said first strobe signal (STB1*) said addressed slave system writes data to said system bus in a read cycle of said master system and, when said addressed slave system receives at least one of said subsequent sequential strobe signals (STB2*...STBn*), sends to said master system an answering signal (RDY*) which causes the master system to read in its read cycle from said system bus the data as output by said addressed slave system and to temporarily terminate sending said first and all of said subsequent, sequential strobe signals and to terminate the address signal until said addressed slave system stops outputting its data to the system bus and renders the answering signal (RDY*) non-active in response to said termination of one of said first and subsequent sequential strobe signals from the master system, and wherein said master system further writes in its write cycle the data which it has already put out to the system bus in the addressed slave system at a time after the answering signal (RDY*) is turned to active. The method of claim 4, wherein said number of said subsequent sequential strobe signals is such that the last of it (STBn*) is delayed from said first signal (STB1*) by a time period in excess of the slowest access time of said plurality of slave systems.

Inventors: MURANO KEIJI, SAKAMOTO MASAFUMI, MURANO, KEIJI, SAKAMOTO, MASAFUMI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G06F13
IPC codes: G06F13