AVR interrupt priority
In the same priority level of the AVR microcontroller, the lower the interrupt vector entry address, the higher its priority. After responding to the interrupt, the AVR microcontroller will disable the system from responding to the remaining interrupts. If the program needs to respond to other interrupt events in an interrupt service routine, you can re-enable the global interrupt with the SEI instruction or _SEI()(IAR), SEI()(ICCAVR) in the interrupt service routine. Otherwise, the AVR microcontroller will only re-enable the global interrupt when it exits the interrupt process.
AVR (at least ATmega16) microcontrollers use a fixed hardware priority mode and do not support software resetting of interrupt priority.
AVR has different interrupt sources. Each interrupt and reset has an independent interrupt vector in program space. All interrupt events have their own enable bits. An interrupt can occur when the enable bit is set and the global interrupt enable bit I of the status register is also set. Depending on the program counter PC, the interrupt may be automatically disabled if the boot lock bit BLB02 or BLB12 is programmed. This feature improves the security of the software. See the description of P247 "Memory Programming" for details.
The lowest address of the program memory area defaults to the reset vector and the interrupt vector. See P43 "Interrupts" for a complete list of vectors. The list also determines the priority of the different interrupts. The lower the address where the vector is located, the higher the priority. RESET has the highest priority and the second is INT0 – External Interrupt Request 0. The interrupt vector can be moved to the beginning of the boot Flash by setting the IVSEL of the MCU Control Register (MCUCR). The programming fuse bit BOOTRST can also move the reset vector to the beginning of the boot flash. See P234 "Support Boot Loader - Read (WW, Read-While-Write) self-programming capability while writing".
The global interrupt enable bit, I, is cleared when any interrupt occurs, thus disabling all other interrupts. User software can set interrupts in the interrupt routine to implement interrupt nesting. At this point all interrupts can interrupt the current interrupt service routine. I is automatically set after the RETI instruction is executed.
There are basically two types of interruptions. The first is triggered by an event and sets the interrupt flag. For these interrupts, the program counter branches to the actual interrupt vector to execute the interrupt handler, and the hardware clears the corresponding interrupt flag. The interrupt flag can also be cleared by writing "1" to it. When an interrupt occurs, if the corresponding interrupt enable bit is "0", the interrupt flag bit is set and remains until the interrupt is executed or cleared by software. Similarly, if the global interrupt flag is cleared, all interrupts that have occurred will not be executed until I is set. The pending interrupts are then executed in order of interrupt priority.
The second type of interrupt is triggered as long as the interrupt condition is met. These interrupts do not require an interrupt flag. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered.
After the AVR exits the interrupt, it always returns to the main program and executes at least one instruction to execute other suspended interrupts. It should be noted that the status register is not automatically saved when entering the interrupt service routine, and will not be automatically restored when the interrupt returns. This work must be done by the user through software.
When the interrupt is disabled using the CLI instruction, the interrupt disable takes effect immediately. No interrupt can occur after executing a CLI instruction, even if it is happening while executing a CLI instruction.
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Digital Visual Interface Cable Connectors
DVI ConnectorWith the advent of technologies such as DVD players, high-definition televisions, and even digital cable, the need for more advanced cables and connectors has increased. Digital Visual Interface (DVI) is one response to the growing need for interconnected systems, enabling digital systems to be connected to an array of displays. Yet DVI cables and connectors can also be complicated, and may lead to confusion between High Definition Multimedia Interface (HDMI) and DVI. Although the two systems have much in common, they service different niches of digital technology.
Digital Visual Interface
Older systems aren`t necessarily outdated systems. Although DVI preceded HDMI, it`s still widely used in both business and domestic settings. DVI connectors are designed to handle digital data transmission, incorporating three transmission channels in every connector link. The maximum bandwidth for data transfer is 165 megahertz, which is enough to relay up to 165 million pixels per second. Data is encoded for effective transfer, but a single link can handle around 4.95 gigabits per second of information. Double links can handle twice that amount.
Because a DVI cable carries information over a 165 megahertz bandwidth, complete digital resolution can be obtained. Using double link connectors increases the speed of transmission, but requires another cable. However, not many devices depend solely on a double link DVI, so this technolgy can be used on an as-desired basis.
Types of DVI Connectors
There are three general categories of DVI cable connectors: DVI-Digital (DVI-D), DVI-Integrated (DVI-I), and DVI-Analog (DVI-A). However, most connectors fall into one of the first two groups.
A standard DVI connector is 37 mm wide and has 24 pins, 12 of which are used for a single link connection. When analog is involved, four additional pins are needed to support the additional lines of an analog signal. It is not possible to cross from a digital source to an analog display or vice versa. In those instances, an integrated connector is probably the best option. There are five common types of DVI connectors.
DVI-I Single Link
This kind of connector has three rows, each with six pins. There are two contacts. Because the connector is integrated, it can be used with both analog and digital applications.
DVI-I Dual Link
A DVI-I dual link connector can also be used with both digital and analog applications, but is configured with more pins to accommodate a dual connection. There are three rows with eight pins each, as well as two contacts.
DVI-D Single Link
Specifically designed for digital applications, a DVI-D single link connector has three rows of six pins, and looks much like a DVI-I single link connector. However, a DVI-D connector has no contacts.
DVI-D Dual Link
Also made specifically for digital applications, a DVI-D dual link features more pins (three rows of eight) for dual connections. Like a DVI-D single link, a DVI-D dual link connector has no contacts.
DVI-A
This particular type of connector can only be used for analog applications, and has three rows of pins. One row has five pins, one has four pins, and the last row has three pins. Like single link connectors, a DVI-A link connector has two contacts.
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