If engineer has ever tried to execute Nuvoton Microcomputer W78E51B Encrypted Heximal Recovery, it is necessary to have a general idea about the Microcomputer W78E51B features:

• Fully static design 8-bit CMOS microcontroller
• Wide supply voltage of 4.5V to 5.5V
• 128 bytes of on-chip scratchpad RAM
• 4 KB On-chip Flash EPROM
• 64 KB program memory address space
• 64 KB data memory address space
• Four 8-bit bi-directional ports

• One extra 4-bit bit-addressable I/O port, additional INT2 / INT3
(available on 44-pin PLCC/QFP package)
• Two 16-bit timer/counters
• One full duplex serial port(UART)
• Watchdog Timer
• Seven sources, two-level interrupt capability
• EMI reduction mode
• Built-in power management
• Code protection mechanism

The W78E51B architecture consists of a core controller surrounded by various registers, five general purpose I/O ports, 128 bytes of RAM, two timer/counters, and a serial port. The processor supports 111 different opcodes and references both a 64K program address space and a 64K data storage space.

In order to be more suitable for I/O, an extra 4-bit bit-addressable port P4 and two external interrupt
INT2 , INT3 has been added to either the PLCC or QFP 44 pin package. And description follows:

INT2 / INT3

Two additional external interrupts, INT2 and INT3 , whose functions are similar to those of external interrupt 0 and 1 in the standard 80C52 after Nuvoton Microcomputer W78E51B Encrypted Heximal Recovery. The functions/status of these interrupts are determined/shown by the bits in the XICON (External Interrupt Control) register. The XICON register is bit-addressable but is not a standard register in the standard 80C52. Its address is at 0C0H. To set/clear bits in the XICON register, one can use the “SETB (/CLR) bit” instruction. For example, “SETB 0C2H” sets the EX2 bit of XICON.

XICON – external interrupt control (C0H)

PX3: External interrupt 3 priority high if set EX3: External interrupt 3 enable if set

IE3: If IT3 = 1, IE3 is set/cleared automatically by hardware when interrupt is detected/serviced IT3: External interrupt 3 is falling-edge/low-level triggered when this bit is set/cleared by software PX2: External interrupt 2 priority high if set

EX2: External interrupt 2 enable if set

IE2: If IT2 = 1, IE2 is set/cleared automatically by hardware when interrupt is detected/serviced IT2: External interrupt 2 is falling-edge/low-level triggered when this bit is set/cleared by software

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