UPD784020 Datasheet, PDF (22/90 Pages) NEC – 16/8-BIT SINGLE-CHIP MICROCOMPUTER

mPD784020, 784021
7.2.2 Control Registers
(1) Program counter (PC)
This register is a 20-bit program counter. The program counter is automatically updated by program execution.
Fig. 7-4 Format of Program Counter (PC)
19
0
PC
(2) Program Status Word (PSW)
This register holds the CPU state. The program status word is automatically updated by program execution.
Fig. 7-5 Format of Program Status Word (PSW)
15
14
13
12
11
10
9
8
PSWH UF RBS2 RBS1 RBS0
PSW
7
PSWL
S
6
5
4
3
2
1
0
Z
RSS^Note AC
IE
P/V
0
CY
Note This flag is used to maintain compatibility with the 78K/III series. This flag must be set to 0 when programs
for the 78K/III series are being used.
(3) Stack pointer (SP)
This register is a 24-bit pointer for holding the start address of the stack. The high-order 4 bits must be set
to 0.
Fig. 7-6 Format of Stack Pointer (SP)
23
20
0
PC
00 00
22