Atmel C51 - Manual (Page 18)

Operation Mode
3-15 C51 Microcontrollers Demo Board User Guide
4119C–8051–3/03
Figure 3-8. C51 Mode (Non Page Mode)
3.3.2 C251 Mode In C251 mode, the microcontroller can be used in Page Mode or Non Page Mode.
For Non Page Mode switch J8 must be in the same configuration as in C51 mode.
For Page Mode switch J8 must be as shown in Figure 3-9.
Figure 3-9. C251 Mode (Page Mode)
J11
J9
J16
J8
NON PAGE MODE
J11
J9
J16
J8
PAGE MODE