Functioning hardware for AT89C2051-24PC consists
of the controller with a crystal and two ceramic capacitors, an
electrolytic capacitor between Vcc and RESET and a 100nF bypass
capacitor on the supply voltages.
The 80C31 has more IO ports, although ports 0 and
2 are already used for connection to the external program memory.
This leaves only ports 1 and 3 available for the application.
Apart from P3.6, these are the same ports that are available with
the AT89C2051-24PC. All other features, such as eg. timers, serial
UART, idle mode and powerdown mode, are 100% compatible.
The AT89C2051-24PC also features an analog
comperator. It has an static processor core, ie. there is no
minimum clock frequency. the maximum clock frequency is 24 MHz. Of
course the AT89C2051-24PC can also be run at 11.0592 MHz.
If more than 2k bytes program memory is required,
type AT89C4051-24PC may be used. This device has 4k bytes memory
and is identical in any other regard. Data
sheet AT89C4051-24PC in PDF-Format from Atmel.