Fujitsu F2MC-16L Series User Manual page 52

FUJITSU MB90675-Evaluation Board - User Manual
Ports P0, P1, P2 and P20..33 of the MB90675 microcontroller are used as an external
microprocessor bus, connecting the Monitor EPROMs U10, U11 and the User RAMs U22,
U23, Address latches U2, U3 are used to de-multiplex the combined address/data bus.
The PAL or GAL U24 is used as a memory decoder and provides chip select signals for the
EPROM (/ROM), User RAM (/RAM), Memory mapped control registers in GAL U16
(/CTRL ) and a select signal (/EXP) which can be used for expanded memory. The enable
signals to set the LED displays latches are also generated there.
The mode registers within U16 control the operation of U24. GAL U6 implements eight
control registers selected by (/CTRL, A1, A2, A3). Four of them are bit wide and read/write
capable using /WRL, /RD, and AD0 (mode register, single LED register). The remaining four
registers are read/write capable using /WRL, /RD and AD0..7 (external UART), write capable
using /WRL, /WRH, AD0..15 (LED displays).
GAL U16 is also used to generate a reset signal on /RES if either the Master Reset Button
(/MRES) or the User Reset Button (/URES) is pressed.
If one of these reset buttons is activated, the Mode registers are either cleared or set (see
Board Controls).
© FUJITSU Mikroelektronik GmbH 1996
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