Strobe Control in Computer Architecture:- The strobe control method of asynchronous data transfer employs a single control line to time each transfer. The strobe may be activated by either the source or the destination unit. The figure shows a source initiated transfer. The data bus carries the binary information rom source unit to the destination unit. Typically, the bus has multiple lines to transfer an entire byte or word. The strobe is a single line that informs the destination unit when a valid data word is available on the bus. In this post, we discuss Strobe Control in Computer Architecture.
As shown in the timing diagram of the figure, the source unit first places the data on the data bus. After a brief delay to ensure that the data settle to a steady value, the source activates the strobe pulse. The information on the data bus and the strobe signal remains in the active state for a sufficient time period to allow the destination unit to receive the data. Often, the destination unit uses the falling edge of the strobe pulse to transfer the contents of the data bus into one of its internal registers. The source removes the data from the bus brief period after it disables its strobe pulse. Actually, the source does not have to change the information in the data bus. The fact that the strobe signal is disabled indicates that the data bus does not contain valid data. New valid data will be available only after the strobe is enabled again.
The figure shows a data transfer initiated by the destination unit. In this case, the destination unit activates the strobe pulse, informing the source to provide the data. The source unit responds by placing the requested binary information on the data bus. The data must be valid and remain on the bus long enough for the destination unit to accept it. The falling edge of the strobe pulse can be used again to trigger a destination register. The destination unit then disables the strobe. The source removes the data from the bus after a predetermined time interval:
In many computers, the strobe pulse is actually controlled by the clock pulses in the CPU. The CPU is always in control of the buses and informs the external units how to transfer data. For example, the strobe first figure could be a memory-write control signal from the CPU to a memory unit. The source, being the CPU, places a word on the data bus and informs the memory unit, which is the destination, that this is a write operation. Similarly, the strobe of the second figure could be a memory-read control signal from the CPU to a memory unit. The destination, the CPU, initiates the read operation to inform the memory, which is the source, to place a selected word into the data bus.
The transfer of data between the CPU and an interface unit is similar to the strobe transfer just described. Data transfer between an interface and an I/0 device is commonly controlled by a set of handshaking lines.