APPENDIX B
Impact of External Program ROM
The 8051 family of microcontrollers, including the industry
standards, use ports 0 and 2 to access external memory. In
implementations with external program memory, these two ports
are dedicated to the program ROM interface and can not be used
as Input/Output ports. The UT69RH051 uses external program
ROM, so ports 0 and 2 will not be available for I/O.
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