UPD784021 datasheet(21/90 Pages) NEC

21 / 90 page

mPD784020, 784021

7.2

CPU REGISTERS

7.2.1

General-Purpose Registers

A set of general-purpose registers consists of sixteen general-purpose 8-bit registers. Two 8-bit general-purpose

registers can be combined to form a 16-bit general-purpose register. Moreover, four 16-bit general-purpose registers,

when combined with an 8-bit register for address extension, can be used as 24-bit address specification registers.

Eight banks of this register set are provided. The user can switch between banks by software or the context

switching function.

General-purpose registers other than the V, U, T, and W registers used for address extension are mapped onto

internal RAM.

Fig. 7-3 General-Purpose Register Format

Caution By setting the RSS bit of PSW to 1, R4, R5, R6, R7, RP2, and RP3 can be used as the X, A, C, B,

AX, and BC registers, respectively. However, this function must be used only when using

programs for the 78K/III series.

A (R1)

X (R0)

B (R3)

C (R2)

R11

R10

D (R13)

E (R12)

H (R15)

L (R14)

AX (RP0)

BC (RP1)

RP2

RP3

VP (RP4)

UP (RP5)

DE (RP6)

HL (RP7)

VVP (RG4)

UUP (RG5)

TDE (RG6)

WHL (RG7)

The character strings enclosed in

parentheses represent absolute names.

8 banks

UPD784021 Datasheet(PDF) 21 Page - NEC