Separate bus communication

Separate bus communication Synchronous communication, asynchronous communication, and semi-synchronous communication start from the address and read/write command issued by the main module until the data transmission is complete. During the entire transmission cycle, the right to use the system bus is fully occupied by the master module and the slave module selected by the system bus. Further analysis of the read command transmission cycle, we found that in addition to applying for the bus, the remaining time is mainly spent in the following three aspects. 1. The main module sends addresses and commands to the slave module through the transmission bus. 2. Prepare the slave module to read data according to the command. 3. Data from the module is provided to the main module through data lines. It can be seen from 2 that for the system bus, there is no substantial information transmission during data reading from the module, and the bus is purely idle waiting. In order to overcome and utilize this kind of negative wait, especially in large-scale computer systems, the bus load is already saturated, and the potential of the system bus is fully explored every moment, which plays a great role in improving the system. Therefore, a separate communication method is proposed. The basic idea is to divide a transmission cycle (or Bus Cycle) into two subcycles. In the first sub-cycle, after obtaining the right to use the bus, main module A includes commands, addresses, and other related information, including the number of the main module (when there are multiple main modules, this number is particularly important) sent to the system bus. After transmission through the bus, it is received by the relevant Slave Module B. It takes only a short time for main module A to publish the information to the system bus. Once the information is sent, the right to use the bus is immediately revoked for other modules to use. In the second subcycle, when Module B receives the relevant command signal from module A, it prepares the data required by module A after a series of internal operations such as selection, decoding, and reading, module B applies for the right to use the bus. Once approved, Module B sends a series of information such as the number of module A, the address of Module B, and the data required for module A to the bus, for receiving by module. Obviously, the above two subcycles only have single-direction information flows, and each module becomes the main module. This communication method has the following features: 1. Each module must apply for the right to use the bus. 2. After obtaining the right to use the bus, the main module sends information to the other party within a limited period of time and uses synchronous transmission instead of waiting for the response from the other party. 3. Each module does not occupy the bus during data preparation. The bus can accept requests from other modules. 4. when the bus is in use, it is doing effective work, or sending commands or transmitting data through it. There is no idle waiting time, making full use of the effective occupation of the bus, this enables cross-overlapping parallel transmission between multiple master and slave modules, which is extremely important for large computers. This control method is complex and rarely used in general microcomputer systems.