W741L250 Datasheet, PDF (8/86 Pages) Winbond – 4-BIT MICROCONTROLLER

W741L250
2. Page Register (PAGE)
The page register is organized as a 4-bit binary register. The bit descriptions are as follows:
3
2
1
0
PAGE ^_ R/W R/W R/W
Note: R/W means read/write available.
Bit 3 is reserved.
Bit 2, Bit 1, Bit 0 are indirect addressing mode preselect bits:
000 = Page 0 (00H−0FH)
010 = Page 2 (20H−2FH)
100 = Page 4 (40H−4FH)
110 = Page 6 (60H−6FH)
001 = Page 1 (10H−1FH)
011 = Page 3 (30H−3FH)
101 = Page 5 (50H−5FH)
111 = Page 7 (70H−7FH)
Accumulator (ACC)
The accumulator (ACC) is a 4-bit register used to hold results from the ALU and transfer data
between the memory, I/O ports, and registers.
Arithmetic and Logic Unit (ALU)
This is a circuit which performs arithmetic and logic operations. The ALU provides the following
functions:
• Logic operations: ANL, XRL, ORL
• Branch decisions: JB0, JB1, JB2, JB3, JNZ, JZ, JC, JNC, DSKZ, DSKNZ, SKB0, SKB1, SKB2,
SKB3
• Shift operations: SHRC, RRC, SHLC, RLC
• Binary additions/subtractions: ADC, SBC, ADD, SUB, ADU, DEC, INC
After any of the above instructions are executed, the status of the carry flag (CF) and zero flag (ZF) is
stored in the internal registers. CF can be read out by executing MOVA R, CF.
Clock Generator
The W741L250 provides a crystal or RC oscillation circuit selected by option codes to generate the
system clock through external connections. If a crystal oscillator is used, a crystal or a ceramic
resonator must be connected to XIN and XOUT, and the capacitor must be connected if an accurate
frequency is needed. When a crystal oscillator is used, only low-frequency clock (32 KHz) can be
selected for the system clock by means of option codes. If the RC oscillator is used, a resistor in the
range of 28 KΩ to 1.6 MΩ must be connected to XIN and XOUT, as shown in Figure 3. The system
clock frequency range is from 32 KHz to 2 MHz. One machine cycle consists of a four-phase system
clock sequence and can run up to 4 µS with a 1 MHz system clock.
Crystal
32 KHz
XIN
XOUT
or Resistor
XIN
XOUT
Figure 3. Oscillator Configuration
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