CS5535 datasheet(106/555 Pages) NSC

106 / 555 page

www.national.com

106

Revision 0.8

PIC Functional Description (Continued)

As illustrated in Figure 4-20, the blocks that make up the

8259A PIC are:

• Read/Write Control Logic

• Interrupt Request Register (IRR)

• In-Service Register (ISR)

• Interrupt Mask Register (IMR)

• Priority Resolver

• Interrupt Sequence

• Data Bus Buffer

• Cascade Buffer/Comparator

Read/Write Control Logic

The function of this block is to accept commands from the

CPU. It contains the four Initialization Command Word reg-

isters, ICW1-ICW4, and three Operation Command Word

registers, OCW1-OCW3, that can be programmed to oper-

ate in various modes.

IRR, ISR, and IMR

Three registers are available to handle interrupts in the

PIC: Interrupt Request Register (IRR), In-Service Register

(ISR), and Interrupt Mask Register (IMR). Each of the three

registers is eight bits wide, where every bit corresponds to

one of the IR0-IR7 input lines.

Priority Resolver

The priority resolver block manages the hardware requests

according to their priority. As several bits may be set in the

IRR simultaneously, the priority encoder passes only the

highest priority bit; ordered in priority 0 through 7 (0 being

the highest).

Interrupt Sequence

The INT output goes directly to the CPU interrupt input.

When an INT signal is activated, the CPU responds with an

Interrupt Acknowledge access that is translated to two

pulses on the INTA input of the PIC. At the first INTA pulse

the highest priority IRR bit is loaded into the corresponding

ISR bit, and that IRR bit is reset. The second INTA pulse

instructs the PIC to present the 8-bit vector of the interrupt

handler onto the data bus.

Data Bus Buffer

Control words and status information are transferred

through the data bus buffer.

Cascade Buffer/Comparator

This functional block stores and compares the IDs of the

PICs.

Figure 4-20. PIC 8259A Block Diagram

Internal Bus

Interrupt Mask Register

(IMR)

In-Service

(ISR)

Priority

Resolver

Interrupt

Request

(IRR)

Control Logic

Data

Bus

Buffer

Read/

Write

Logic

Cascade

Buffer/

Comparator

INTA

INT

D7-D0

CAS0

CAS1

CAS2

SP/EN

IR0

IR1

IR2

IR3

IR4

IR5

IR6

IR7

CS5535 датащи(PDF) 106 Page - National Semiconductor (TI)

CS5535 датащи(HTML) 106 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL