Page Mode

The MCBx51 board provides complete support for 251 Page and Non-page (NONP) mode. To do this, the MCBx51 board includes 2 latches for the data/address bus.

In NONP mode, the 251/151 multiplexes the address bus (A0-A7) and data bus (D0-D7) on port 0. This works the same way as the standard 8051. To support NONP mode, the configuration jumpers must be in the NONP position. In NONP mode, the address bus (port 0) is latched using the 74HC373 at IC8.

In Page mode, the 251/151 multiplexes the address bus (A8-A15) and data bus (D0-D7) on port 2. To support Page mode, the configuration jumpers must be in the Page position. In Page mode, the address bus (port 2) is latched using the 74HC373 at IC15.

Notes

• The microcontroller configuration bytes must be set according to the board configuration for Page or NONP mode. Refer to the 251/151 data sheet for more information about the microcontroller configuration bytes.
• The Monitor EPROM contains pre-configured Monitor versions for Page and NONP mode. These are selected with the Page DIP switch. To select a Monitor version for Page mode, the Page DIP switch must be ON.