These types of interface circuits must include buffer registers to ensure that data remains in the interface long enough to meet the timing requirements of external devices—or to enable the microprocessor to access and retrieve data at precisely the right moments. Additionally, they should incorporate various control circuits, such as address decoding and selection circuits, status flag circuits that respond when queried by the MPU, and circuits directly controlled by the MPU itself. These also include registers designed to store control commands sent from the MPU, as well as interrupt logic control circuits, and more.
Commonly used is the method of transmitting several binary digits that make up a single character simultaneously over multiple parallel channels. In parallel transmission, a character can be sent at once, eliminating the need for synchronization between the sender and receiver. Additionally, this method is fast and features simple control mechanisms. However, parallel transmission requires multiple physical channels. Therefore, it’s best suited for short-distance applications where high-speed data transfer is essential.
The concept of parallel transmission
Parallel transmission refers to the process of sending data in groups simultaneously over multiple parallel channels. A common approach involves transmitting the individual binary bits that make up a single character across several parallel channels at once. Additionally, a control signal—known as the "gate" pulse—is sent after the data signals are initiated. This pulse serves to inform the receiving device that all bits have been successfully transmitted, allowing it to begin sampling the signals on each channel.
This type of transmission is relatively simple: for an 8-bit microprocessor, 8 bits of data are sent simultaneously in a single transfer. Since the microprocessor itself performs parallel processing on the data it handles, there’s no need to convert the data format. As a result, the interface circuitry required to implement this type of transmission is also quite straightforward.
The basic principle of parallel transmission
Encoding for parallel transmission
A coded character is typically represented by several binary digits— for example, a symbol encoded using ASCII requires 8-bit binary numbers. As a result, transmitting an ASCII-encoded symbol in parallel would necessitate 8 separate transmission channels, allowing all the data bits that make up the symbol to travel simultaneously, each along its own dedicated channel. In parallel transmission, a single character can be sent at once, eliminating the need for synchronization between sender and receiver. Additionally, this method is fast and easy to control. However, parallel transmission demands multiple physical channels, making it suitable only for short-distance applications where high-speed data transfer is critical.
The type of interface circuits must include buffer registers to ensure that data remains in the interface long enough to accommodate the timing requirements of external devices—or to allow the microprocessor to access and retrieve data at the right moments. Additionally, they should incorporate various control circuits, such as address decoding and selection circuits, status flag circuits that respond when queried by the MPU, and circuits controlled by the MPU itself. These also include registers designed to store control commands sent from the MPU, as well as interrupt logic control circuits, and more.
Implementation of parallel transmission
An 8-unit binary code is used to represent a single character for parallel transmission. The system employs eight parallel channels, allowing one character to be sent simultaneously. As a result, there’s no need for character synchronization between the sender and receiver—no additional measures are required to ensure both sides stay in sync. This is one of the key advantages of parallel transmission. However, parallel transmission demands multiple parallel channels, which significantly increases costs and makes it less suitable for long-distance communication.
These types of buses offer high-speed data transmission but are best suited for short-distance communication. Typical examples include the S-100 bus, MUI.TIBUS bus, standard bus, and IEEE-488 bus. Parallel standard buses are usually used to connect individual plug-in boards, while the IEEE-488 bus is specifically designed for linking entire systems together.