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CD82C59A Arkusz danych(PDF) 5 Page - Intersil Corporation |
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CD82C59A Arkusz danych(HTML) 5 Page - Intersil Corporation |
5 / 20 page 4-5 Priority Resolver This logic block determines the priorities of the bits set in the lRR. The highest priority is selected and strobed into the cor- responding bit of the lSR during the INTA sequence. Interrupt Mask Register (IMR) The lMR stores the bits which disable the interrupt lines to be masked. The IMR operates on the output of the IRR. Masking of a higher priority input will not affect the interrupt request lines of lower priority. Interrupt (INT) This output goes directly to the CPU interrupt input. The VOH level on this line is designed to be fully compatible with the 8080, 8085, 8086/88, 80C86/88, 80286, and 80C286 input levels. Interrupt Acknowledge (INTA) INTA pulses will cause the 82C59A to release vectoring information onto the data bus. The format of this data depends on the system mode ( µPM) of the 82C59A. Data Bus Buffer This 3-state, bidirectional 8-bit buffer is used to interface the 82C59A to the System Data Bus. Control words and status information are transferred through the Data Bus Buffer. Read/Write Control Logic The function of this block is to accept output commands from the CPU. It contains the Initialization Command Word (lCW) registers and Operation Command Word (OCW) registers which store the various control formats for device operation. This function block also allows the status of the 82C59A to be transferred onto the Data Bus. Chip Select (CS) A LOW on this input enables the 82C59A. No reading or writing of the device will occur unless the device is selected. Write (WR) A LOW on this input enables the CPU to write control words (lCWs and OCWs) to the 82C59A. Read (RD) A LOW on this input enables the 82C59A to send the status of the Interrupt Request Register (lRR), In-Service Register (lSR), the Interrupt Mask Register (lMR), or the interrupt level (in the poll mode) onto the Data Bus. A0 This input signal is used in conjunction with WR and RD sig- nals to write commands into the various command registers, as well as to read the various status registers of the chip. This line can be tied directly to one of the system address lines. The Cascade Buffer/Comparator This function block stores and compares the IDs of all 82C59As used in the system. The associated three I/O pins (CAS0 - 2) are outputs when the 82C59A is used as a mas- ter and are inputs when the 82C59A is used as a slave. As a master, the 82C59A sends the ID of the interrupting slave device onto the CAS0 - 2 lines. The slave, thus selected will send its preprogrammed subroutine address onto the Data Bus during the next one or two consecutive INTA pulses. (See section “Cascading the 82C59A”.) Interrupt Sequence The powerful features of the 82C59A in a microcomputer system are its programmability and the interrupt routine addressing capability. The latter allows direct or indirect jumping to the specified interrupt routine requested without any polling of the interrupting devices. The normal sequence of events during an interrupt depends on the type of CPU being used. These events occur in an 8080/8085 system: 1. One or more of the INTERRUPT REQUEST lines (IR0 - IR7) are raised high, setting the corresponding IRR bit(s). 2. The 82C59A evaluates those requests in the priority resolver and sends an interrupt (INT) to the CPU, if appropriate. 3. The CPU acknowledges the lNT and responds with an INTA pulse. 4. Upon receiving an lNTA from the CPU group, the highest priority lSR bit is set, and the corresponding lRR bit is reset. The 82C59A will also release a CALL instruction code (11001101) onto the 8-bit data bus through D0 - D7. 5. This CALL instruction will initiate two additional INTA pulses to be sent to 82C59A from the CPU group. 6. These two INTA pulses allow the 82C59A to release its preprogrammed subroutine address onto the data bus. The lower 8-bit address is released at the first INTA pulse and the higher 8-bit address is released at the second INTA pulse. 7. This completes the 3-byte CALL instruction released by the 82C59A. In the AEOI mode, the lSR bit is reset at the end of the third INTA pulse. Otherwise, the lSR bit remains set until an appropriate EOI command is issued at the end of the interrupt sequence. The events occurring in an 80C86/88/286 system are the same until step 4. 4. The 82C59A does not drive the data bus during the first INTA pulse. 5. The 80C86/88/286 CPU will initiate a second INTA pulse. During this INTA pulse, the appropriate ISR bit is set and the corresponding bit in the IRR is reset. The 82C59A outputs the 8-bit pointer onto the data bus to be read by the CPU. 82C59A |
Podobny numer części - CD82C59A |
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Podobny opis - CD82C59A |
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