11
MITSUBISHI MICROCOMPUTERS
4250 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
Fig. 1 AMC instruction execution example
Fig. 2 RAR instruction execution example
Fig. 3 Registers A, B and register E
(CY)
(M(DP))
(A)
Addition
ALU
<Carry>
<Result>
CY
A3 A2 A1 A0
A0
CY A3 A2 A1
<Rotation>
RAR instruction
<Set>
SC instruction
<Clear>
RC instruction
A3 A2 A1 A0
B3 B2 B1 B0
E7 E6 E5 E4 E3 E2 E1 E0
A3 A2 A1 A0
B3 B2 B1 B0
TAB instruction
TEAB instruction
TABE instruction
TBA instruction
Register B
Register A
Register B
Register A
Register E
Fig. 4 TABP p instruction execution example
FUNCTION BLOCK OPERATIONS
CPU
(1) Arithmetic logic unit (ALU)
The arithmetic logic unit ALU performs 4-bit arithmetic such
as 4-bit data addition, comparison, and bit manipulation.
(2) Register A and carry flag
Register A is a 4-bit register used for arithmetic, transfer,
exchange, and I/O operation.
Carry flag CY is a 1-bit flag that is set to “1” when there is a
carry with the AMC instruction (Figure 1).
It is unchanged with both A n instruction and AM instruction.
The value of A0 is stored in carry flag CY with the RAR
instruction (Figure 2).
Carry flag CY can be set to “1” with the SC instruction and
cleared to “0” with the RC instruction.
(3) Registers B and E
Register B is a 4-bit register used for temporary storage of 4-
bit data, and for 8-bit data transfer together with register A.
Register E is an 8-bit register. It can be used for 8-bit data
transfer with register B used as the high-order 4 bits and
register A as the low-order 4 bits (Figure 3).
(4) Register D
Register D is a 3-bit register.
It is used to store a 7-bit ROM address together with register
A and is used as a pointer within the specified page when the
TABP p, BLA p, or BMLA p instruction is executed (Figure 4).
Specifying address
TABP p instruction
p3 p2 p1 p0
PCH
DR2 DR1 DR0 A3 A2 A1 A0
PCL
Immediate field
value p
The contents of
register D
ROM
84
0
Middle-order 4 bits
Low-order 4 bits
Register A (4)
Register B (4)
The contents of
register A