Ao of the A is connected to system line Al. The data lines of an are connected to the lower half of the system data bus; because the expects to receive interrupt types on these lower eight data lines. The eight IR inputs are available for interrupt signals. Cascading : The can be easily interconnected to get multiple interrupts. Fig below shows how can be connected in the cascade mode. In cascade mode one is configured in Master mode and other should be configured in the Slave mode.
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The A0 input of the A is used to select one of the two internal addresses in the device: A0 of the A is connected to system line A0. So the system addresses for the two internal addresses are F0H and F1H. The eight IR inputs are available for interrupt signals. Note : Unused IR inputs should be tied to ground so that a noise pulse cannot accidentally cause an interrupt.
The A0 input of the A is used to select one of the two internal addresses in the device. A0 of the A is connected to system line A1. Cascading: The A can be easily interconnected to get multiple interrupts. In cascade mode one A is configured in Master mode and other should be configured in the Slave mode. In this figure A-1 is in the master mode and others are in slave mode. Each slave A is identified by the number which is assigned as a part of its initialization.
These cascaded As are referred to as slave. For the master these pins function as outputs, and for the slave these pins function as inputs. However, it is grounded for the slave. Each A has its own addresses so that command words can be written to it and status bytes read from it. Addresses for As : Master and slave operation : When the slave receives an interrupt signal on one of its IR inputs, it checks mask condition and priority of the interrupt request. If the interrupt is unmasked and its priority is higher than any other interrupt level being serviced in the slave, then the slave will send an INT signal to the IR input of a master.
Sending the 3-bit ID number enables the slave. When the slave receives the second INTA pulse from the , the slave will send the low-order address byte of the ISR on the data bus. If an interrupt signal is applied directly to one of the IR inputs of the master, the master will send the opcode for CALL instruction to the when it receives the first INTA pulse from the It then sends low-order byte and high-order byte in successive interrupt acknowledge cycles second and third.
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