ST62T35B ST Microelectronics, ST62T35B Datasheet - Page 16

• Manufacturer Part Number: ST62T35B
• Description: (ST62E35B / ST62T35B) 8-BIT OTP/EPROM MCUs
• Manufacturer: ST Microelectronics

15
ST62T35B/E35B
2 CENTRAL PROCESSING UNIT
2.1 INTRODUCTION
The CPU Core of ST6 devices is independent of
the I/O or Memory configuration. As such, it may be
thought of as an independent central processor
communicating with on-chip I/O, Memory and Pe-
ripherals via internal address, data, and control
buses. In-core communication is arranged as
shown in Figure 6; the controller being externally
linked to both the Reset and Oscillator circuits,
while the core is linked to the dedicated on-chip pe-
ripherals via the serial data bus and indirectly, for
interrupt purposes, through the control registers.
2.2 CPU REGISTERS
The ST6 Family CPU core features six registers and
three pairs of flags available to the programmer.
These are described in the following paragraphs.
Accumulator (A). The accumulator is an 8-bit
general purpose register used in all arithmetic cal-
culations, logical operations, and data manipula-
tions. The accumulator can be addressed in Data
space as a RAM location at address FFh. Thus
the ST6 can manipulate the accumulator just like
any other register in Data space.
Figure 6ST6 Core Block Diagram
16/82
ROM/EPROM
PROGRAM
12
OPCODE
RESET
6 LAYER STACK
Program Counter
and
CONTROLLER
VALUES
FLAG
OSCin
FLAGS
0,01 TO 8MHz
2
A-DATA
CONTROL
SIGNALS
OSCout
ALU
B-DATA
Indirect Registers (X, Y). These two indirect reg-
isters are used as pointers to memory locations in
Data space. They are used in the register-indirect
addressing mode. These registers can be ad-
dressed in the data space as RAM locations at ad-
dresses 80h (X) and 81h (Y). They can also be ac-
cessed with the direct, short direct, or bit direct ad-
dressing modes. Accordingly, the ST6 instruction
set can use the indirect registers as any other reg-
ister of the data space.
Short Direct Registers (V, W). These two regis-
ters are used to save a byte in short direct ad-
dressing mode. They can be addressed in Data
space as RAM locations at addresses 82h (V) and
83h (W). They can also be accessed using the di-
rect and bit direct addressing modes. Thus, the
ST6 instruction set can use the short direct regis-
ters as any other register of the data space.
Program Counter (PC). The program counter is a
12-bit register which contains the address of the
next ROM location to be processed by the core.
This ROM location may be an opcode, an oper-
and, or the address of an operand. The 12-bit
length allows the direct addressing of 4096 bytes
in Program space.
ADDRESS/READ LINE
DECODER
ADDRESS
RESULTS TO DATA SPACE (WRITE LINE)
INTERRUP TS
256
ACCUMULATOR
DEDICATION S
RAM/EE PROM
ROM/EPROM
DATA SPACE
DATA
DATA
VR01811