UPD784020 Datasheet, PDF (21/90 Pages) NEC – 16/8-BIT SINGLE-CHIP MICROCOMPUTER

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
A (R1)
X (R0)
AX (RP0)
B (R3)
C (R2)
BC (RP1)
R5
R4
RP2
R7
R6
RP3
V
R9
R8
VVP (RG4) VP (RP4)
U
R11
R10
UUP (RG5) UP (RP5)
T
D (R13)
E (R12)
TDE (RG6) DE (RP6)
W
H (R15)
L (R14)
WHL (RG7) HL (RP7)
The character strings enclosed in
parentheses represent absolute names.
8 banks
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.
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