PD780133 datasheet(68/558 Pages) NEC

68 / 558 page

CHAPTER 3 CPU ARCHITECTURE

User’s Manual U16228EJ2V0UD

3.2 Processor Registers

The 78K0/KE1 products incorporate the following processor registers.

3.2.1 Control registers

The control registers control the program sequence, statuses and stack memory. The control registers consist of a

program counter (PC), a program status word (PSW) and a stack pointer (SP).

(1) Program counter (PC)

The program counter is a 16-bit register that holds the address information of the next program to be executed.

In normal operation, the PC is automatically incremented according to the number of bytes of the instruction to be

fetched. When a branch instruction is executed, immediate data and register contents are set.

RESET input sets the reset vector table values at addresses 0000H and 0001H to the program counter.

Figure 3-17. Format of Program Counter

PC15 PC14 PC13 PC12 PC11 PC10 PC9

PC8

PC7

PC6

PC5

PC4

PC3

PC2

PC1

PC0

(2) Program status word (PSW)

The program status word is an 8-bit register consisting of various flags set/reset by instruction execution.

Program status word contents are automatically stacked upon interrupt request generation or PUSH PSW

instruction execution and are restored upon execution of the RETB, RETI and POP PSW instructions.

RESET input sets the PSW to 02H.

Figure 3-18. Format of Program Status Word

PSW

RBS1

RBS0

ISP

(a) Interrupt enable flag (IE)

This flag controls the interrupt request acknowledge operations of the CPU.

When 0, the IE flag is set to the interrupt disabled (DI) state, and all maskable interrupt requests are

disabled. Other interrupt requests are all disabled.

When 1, the IE flag is set to the interrupt enabled (EI) state and interrupt request acknowledgement is

controlled with an in-service priority flag (ISP), an interrupt mask flag for various interrupt sources, and a

priority specification flag.

The IE flag is reset (0) upon DI instruction execution or interrupt acknowledgement and is set (1) upon EI

instruction execution.

PD780133 Datasheet(PDF) 68 Page - NEC

PD780133 Datasheet(HTML) 68 Page - NEC

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

Datasheet Download

Link URL