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MD82C59AB Datasheet(PDF) 7 Page - Intersil Corporation |
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MD82C59AB Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 20 page 4-7 80C86, 8OC88, 80C286 Interrupt Response Mode 80C86/88/286 mode is similar to 8080/85 mode except that only two Interrupt Acknowledge cycles are issued by the pro- cessor and no CALL opcode is sent to the processor. The first interrupt acknowledge cycle is similar to that of 8080/85 systems in that the 82C59A uses it to internally freeze the state of the interrupts for priority resolution and, as a master, it issues the interrupt code on the cascade lines. On this first cycle, it does not issue any data to the processor and leaves its data bus buffers disabled. On the second interrupt acknowledge cycle in the 86/88/286 mode, the master (or slave if so programmed) will send a byte of data to the pro- cessor with the acknowledged interrupt code composed as follows (note the state of the ADI mode control is ignored and A5 - A11 are unused in the 86/88/286 mode). Programming the 82C59A The 82C59A accepts two types of command words gener- ated by the CPU: 1. Initialization Command Words (ICWs): Before normal operation can begin, each 82C59A in the system must be brought to a starting point - by a sequence of 2 to 4 bytes timed by WR pulses. 2. Operation Command Words (OCWs): These are the command words which command the 82C59A to operate in various interrupt modes. Among these modes are: a. Fully nested mode. b. Rotating priority mode. c. Special mask mode. d. Polled mode. The OCWs can be written into the 82C59A anytime after ini- tialization. Initialization Command Words (lCWs) General Whenever a command is issued with A0 = 0 and D4 = 1, this is interpreted as Initialization Command Word 1 (lCW1). lCW1 starts the initialization sequence during which the fol- lowing automatically occur: a. The edge sense circuit is reset, which means that follow- ing initialization, an interrupt request (IR) input must make a low-to-high transition to generate an interrupt. b. The Interrupt Mask Register is cleared. c. lR7 input is assigned priority 7. d. Special Mask Mode is cleared and Status Read is set to lRR. e. If lC4 = 0, then all functions selected in lCW4 are set to zero. (Non-Buffered mode (see note), no Auto-EOI, 8080/85 system). NOTE: Master/Slave in ICW4 is only used in the buffered mode. Initialization Command Words 1 and 2 (ICW1, lCW2) A5 - A15: Page starting address of service routines. In an 8080/85 system the 8 request levels will generate CALLS to 8 locations equally spaced in memory. These can be pro- grammed to be spaced at intervals of 4 or 8 memory loca- tions, thus, the 8 routines will occupy a page of 32 or 64 bytes, respectively. CONTENT OF THIRD INTERRUPT VECTOR BYTE D7 D6 D5 D4 D3 D2 D1 D0 A15 A14 A13 A12 A11 A10 A9 A8 CONTENT OF INTERRUPT VECTOR BYTE FOR 80C86/88/286 SYSTEM MODE D7 D6 D5 D4 D3 D2 D1 D0 lR7 T7 T6 T5 T4 T3 1 1 1 lR6 T7 T6 T5 T4 T3 1 1 0 IR5 T7 T6 T5 T4 T3 1 0 1 IR4 T7 T6 T5 T4 T3 1 0 0 IR3 T7 T6 T5 T4 T3 0 1 1 IR2 T7 T6 T5 T4 T3 0 1 0 IR1 T7 T6 T5 T4 T3 0 0 1 IR0 T7 T6 T5 T4 T3 0 0 0 ICW1 ICW2 IN CASCADE MODE ICW3 IS ICW4 NEEDED ICW4 READY TO ACCEPT INTERRUPT REQUESTS NO (SNGL = 1) YES (SNGL = 0)) YES (IC4 = 1) NO (IC4 = 0) FIGURE 6. 82C59A INITIALIZATION SEQUENCE 82C59A |
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