Architecture of the 8051 Family
The 8051 is an 8-bit, low-power, high-performance microcontroller. There are a large number of devices in the 8051 family with similar architecture and each member of the family is downward compatible with each other. The basic 8051 microcontroller has the following features:
• 4 Kbytes of program memory
• 256 x 8 RAM data memory
• 32 programmable I/O lines
• Two16-bit timer/counters
• Six interrupt sources
• Programmable serial UART port
• External memory interface
• Standard 40-pin package
The EPROM versions of the family (e.g. 8751) are used for development and the program memory of these devices is erased with an ultraviolet light source. The pin configuration of the standard 8051 microcontroller is shown in Fig. 1.1.
The AT89C2051 is a low-end member of the 8051 family, aimed for less complex applications. This device contains a 2 Kbyte flash programmable memory (PEROM) which can be erased and reprogrammed using a suitable programmer. The AT89C2051 contains 128 bytes of RAM and 15 program- mable I/O lines. The code developed for this device runs on a standard 8051 without any modification. As shown in Fig. 1.2, the AT89C2051 is housed in a 20-pin package.